From a84aca97e25c3dc34a50a70926e301de91037c16 Mon Sep 17 00:00:00 2001
From: Fedor <fedor@mail.ru>
Date: Wed, 9 Sep 2020 17:29:41 +0300
Subject: [PATCH] Next part 2 of the Implement module type scripting.

---
 dom/base/nsDocument.cpp                       |  13 +
 dom/base/nsIDocument.h                        |   2 +
 dom/html/HTMLScriptElement.cpp                |  23 +-
 dom/html/HTMLScriptElement.h                  |   2 +-
 dom/script/ModuleLoadRequest.cpp              |  45 +-
 dom/script/ModuleLoadRequest.h                |  33 +-
 dom/script/ModuleScript.cpp                   |  43 +-
 dom/script/ModuleScript.h                     |  12 +-
 dom/script/ScriptElement.cpp                  |   8 +-
 dom/script/ScriptLoader.cpp                   | 692 ++++++++++--------
 dom/script/ScriptLoader.h                     |  89 ++-
 dom/script/nsIScriptElement.h                 |  29 +-
 dom/script/nsIScriptLoaderObserver.idl        |   9 +-
 dom/svg/SVGScriptElement.cpp                  |   2 +-
 dom/svg/SVGScriptElement.h                    |   2 +-
 dom/xslt/xslt/txMozillaXMLOutput.cpp          |   2 +-
 js/public/Class.h                             |   2 +-
 js/src/builtin/Module.js                      | 300 ++++----
 js/src/builtin/ModuleObject.cpp               | 121 +--
 js/src/builtin/ModuleObject.h                 |  33 +-
 js/src/builtin/SelfHostingDefines.h           |  22 +-
 js/src/builtin/TestingFunctions.cpp           |   8 +-
 js/src/jit-test/tests/modules/bug-1284486.js  |  12 +-
 .../jit-test/tests/modules/bug-1420420-2.js   |  19 +
 .../jit-test/tests/modules/bug-1420420-3.js   |   9 +
 .../jit-test/tests/modules/bug-1420420-4.js   |  16 +
 js/src/jit-test/tests/modules/bug-1420420.js  |  19 +
 js/src/js.msg                                 |   1 -
 js/src/jsapi.cpp                              |  27 +-
 js/src/jsapi.h                                |  22 +-
 js/src/shell/js.cpp                           |  33 +-
 js/src/vm/EnvironmentObject.cpp               |   2 +-
 js/src/vm/GlobalObject.h                      |  14 -
 js/src/vm/Runtime.cpp                         |   6 +-
 js/src/vm/Runtime.h                           |   3 +
 js/src/vm/SelfHosting.cpp                     |  28 +-
 parser/html/nsHtml5SpeculativeLoad.cpp        |  11 +-
 parser/html/nsHtml5SpeculativeLoad.h          |  13 +-
 parser/html/nsHtml5TreeBuilderCppSupplement.h |  16 +-
 parser/html/nsHtml5TreeOpExecutor.cpp         |   6 +-
 parser/html/nsHtml5TreeOpExecutor.h           |   4 +-
 parser/html/nsHtml5TreeOperation.cpp          |   2 +-
 42 files changed, 1012 insertions(+), 743 deletions(-)
 create mode 100644 js/src/jit-test/tests/modules/bug-1420420-2.js
 create mode 100644 js/src/jit-test/tests/modules/bug-1420420-3.js
 create mode 100644 js/src/jit-test/tests/modules/bug-1420420-4.js
 create mode 100644 js/src/jit-test/tests/modules/bug-1420420.js

diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index dc4b23f2c..76490e6b4 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -12446,3 +12446,16 @@ nsIDocument::GetSelection(ErrorResult& aRv)
 
   return nsGlobalWindow::Cast(window)->GetSelection(aRv);
 }
+
+bool
+nsIDocument::ModuleScriptsEnabled()
+{
+  static bool sEnabledForContent = false;
+  static bool sCachedPref = false;
+  if (!sCachedPref) {
+    sCachedPref = true;
+    Preferences::AddBoolVarCache(&sEnabledForContent, "dom.moduleScripts.enabled", false);
+  }
+
+  return nsContentUtils::IsChromeDoc(this) || sEnabledForContent;
+}
\ No newline at end of file
diff --git a/dom/base/nsIDocument.h b/dom/base/nsIDocument.h
index 33aac3a3d..7c1f5b584 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -2830,6 +2830,8 @@ public:
   virtual void ScheduleIntersectionObserverNotification() = 0;
   virtual void NotifyIntersectionObservers() = 0;
 
+  bool ModuleScriptsEnabled();
+
   bool ShouldThrowOnDynamicMarkupInsertion()
   {
     return mThrowOnDynamicMarkupInsertionCounter;
diff --git a/dom/html/HTMLScriptElement.cpp b/dom/html/HTMLScriptElement.cpp
index 5b727280f..f1463d6aa 100644
--- a/dom/html/HTMLScriptElement.cpp
+++ b/dom/html/HTMLScriptElement.cpp
@@ -280,12 +280,20 @@ HTMLScriptElement::GetScriptCharset(nsAString& charset)
 }
 
 void
-HTMLScriptElement::FreezeUriAsyncDefer()
+HTMLScriptElement::FreezeExecutionAttrs(nsIDocument* aOwnerDoc)
 {
   if (mFrozen) {
     return;
   }
 
+  MOZ_ASSERT(!mIsModule && !mAsync && !mDefer && !mExternal);
+
+  // Determine whether this is a classic script or a module script.
+  nsAutoString type;
+  GetScriptType(type);
+  mIsModule = aOwnerDoc->ModuleScriptsEnabled() &&
+              !type.IsEmpty() && type.LowerCaseEqualsASCII("module");
+
   // variation of this code in nsSVGScriptElement - check if changes
   // need to be transfered when modifying.  Note that we don't use GetSrc here
   // because it will return the base URL when the attr value is "".
@@ -300,14 +308,13 @@ HTMLScriptElement::FreezeUriAsyncDefer()
 
     // At this point mUri will be null for invalid URLs.
     mExternal = true;
-
-    bool defer, async;
-    GetAsync(&async);
-    GetDefer(&defer);
-
-    mDefer = !async && defer;
-    mAsync = async;
   }
+  
+  bool defer, async;
+  GetAsync(&async);
+  mAsync = (mExternal || mIsModule) && async;
+  GetDefer(&defer);
+  mDefer = mExternal && !async && defer;
 
   mFrozen = true;
 }
diff --git a/dom/html/HTMLScriptElement.h b/dom/html/HTMLScriptElement.h
index 6edeb9832..198df1ed0 100644
--- a/dom/html/HTMLScriptElement.h
+++ b/dom/html/HTMLScriptElement.h
@@ -41,7 +41,7 @@ public:
   virtual bool GetScriptType(nsAString& type) override;
   virtual void GetScriptText(nsAString& text) override;
   virtual void GetScriptCharset(nsAString& charset) override;
-  virtual void FreezeUriAsyncDefer() override;
+  virtual void FreezeExecutionAttrs(nsIDocument* aOwnerDoc) override;
   virtual CORSMode GetCORSMode() const override;
 
   // nsIContent
diff --git a/dom/script/ModuleLoadRequest.cpp b/dom/script/ModuleLoadRequest.cpp
index d62214304..743f30fb9 100644
--- a/dom/script/ModuleLoadRequest.cpp
+++ b/dom/script/ModuleLoadRequest.cpp
@@ -17,26 +17,54 @@ NS_INTERFACE_MAP_END_INHERITING(ScriptLoadRequest)
 NS_IMPL_CYCLE_COLLECTION_INHERITED(ModuleLoadRequest, ScriptLoadRequest,
                                    mBaseURL,
                                    mLoader,
-                                   mParent,
                                    mModuleScript,
                                    mImports)
 
 NS_IMPL_ADDREF_INHERITED(ModuleLoadRequest, ScriptLoadRequest)
 NS_IMPL_RELEASE_INHERITED(ModuleLoadRequest, ScriptLoadRequest)
 
-ModuleLoadRequest::ModuleLoadRequest(nsIScriptElement* aElement,
+ModuleLoadRequest::ModuleLoadRequest(nsIURI* aURI,
+                                     nsIScriptElement* aElement,
                                      uint32_t aVersion,
                                      CORSMode aCORSMode,
                                      const SRIMetadata &aIntegrity,
+                                     nsIURI* aReferrer,
+                                     mozilla::net::ReferrerPolicy aReferrerPolicy,
                                      ScriptLoader* aLoader)
   : ScriptLoadRequest(ScriptKind::Module,
+                      aURI,
                       aElement,
                       aVersion,
                       aCORSMode,
-                      aIntegrity),
+                      aIntegrity,
+                      aReferrer,
+                      aReferrerPolicy),
     mIsTopLevel(true),
-    mLoader(aLoader)
-{}
+    mLoader(aLoader),
+    mVisitedSet(new VisitedURLSet())
+{
+  mVisitedSet->PutEntry(aURI);
+}
+
+ModuleLoadRequest::ModuleLoadRequest(nsIURI* aURI,
+                                     ModuleLoadRequest* aParent)
+  : ScriptLoadRequest(ScriptKind::Module,
+                      aURI,
+                      aParent->mElement,
+                      aParent->mJSVersion,
+                      aParent->mCORSMode,
+                      SRIMetadata(),
+                      aParent->mURI,
+                      aParent->mReferrerPolicy),
+    mIsTopLevel(false),
+    mLoader(aParent->mLoader),
+    mVisitedSet(aParent->mVisitedSet)
+{
+  MOZ_ASSERT(mVisitedSet->Contains(aURI));
+
+  mIsInline = false;
+  mScriptMode = aParent->mScriptMode;
+}
 
 void ModuleLoadRequest::Cancel()
 {
@@ -83,7 +111,7 @@ ModuleLoadRequest::ModuleLoaded()
   // been loaded.
 
   mModuleScript = mLoader->GetFetchedModule(mURI);
-  if (!mModuleScript || mModuleScript->IsErrored()) {
+  if (!mModuleScript || mModuleScript->HasParseError()) {
     ModuleErrored();
     return;
   }
@@ -95,7 +123,7 @@ void
 ModuleLoadRequest::ModuleErrored()
 {
   mLoader->CheckModuleDependenciesLoaded(this);
-  MOZ_ASSERT(!mModuleScript || mModuleScript->IsErrored());
+  MOZ_ASSERT(!mModuleScript || mModuleScript->HasParseError());
 
   CancelImports();
   SetReady();
@@ -132,8 +160,7 @@ ModuleLoadRequest::LoadFinished()
 {
   mLoader->ProcessLoadedModuleTree(this);
   mLoader = nullptr;
-  mParent = nullptr;
 }
 
 } // dom namespace
-} // mozilla namespace
\ No newline at end of file
+} // mozilla namespace
diff --git a/dom/script/ModuleLoadRequest.h b/dom/script/ModuleLoadRequest.h
index 7b06dd2cf..eefb7dad5 100644
--- a/dom/script/ModuleLoadRequest.h
+++ b/dom/script/ModuleLoadRequest.h
@@ -8,6 +8,7 @@
 #define mozilla_dom_ModuleLoadRequest_h
 
 #include "mozilla/dom/ScriptLoader.h"
+#include "nsURIHashKey.h"
 #include "mozilla/MozPromise.h"
 
 namespace mozilla {
@@ -16,6 +17,16 @@ namespace dom {
 class ModuleScript;
 class ScriptLoader;
 
+// A reference counted set of URLs we have visited in the process of loading a
+// module graph.
+class VisitedURLSet : public nsTHashtable<nsURIHashKey>
+{
+  NS_INLINE_DECL_REFCOUNTING(VisitedURLSet)
+
+private:
+  ~VisitedURLSet() = default;
+};
+
 // A load request for a module, created for every top level module script and
 // every module import. Load request can share a ModuleScript if there are
 // multiple imports of the same module.
@@ -31,12 +42,20 @@ public:
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(ModuleLoadRequest, ScriptLoadRequest)
 
-  ModuleLoadRequest(nsIScriptElement* aElement,
+  // Create a top-level module load request.
+  ModuleLoadRequest(nsIURI* aURI,
+                    nsIScriptElement* aElement,
                     uint32_t aVersion,
                     CORSMode aCORSMode,
                     const SRIMetadata& aIntegrity,
+                    nsIURI* aReferrer,
+                    mozilla::net::ReferrerPolicy,
                     ScriptLoader* aLoader);
 
+  // Create a module load request for an imported module.
+  ModuleLoadRequest(nsIURI* aURI,
+                    ModuleLoadRequest* aParent);
+
   bool IsTopLevel() const {
     return mIsTopLevel;
   }
@@ -55,7 +74,7 @@ private:
 
 public:
   // Is this a request for a top level module script or an import?
-  bool mIsTopLevel;
+  const bool mIsTopLevel;
 
   // The base URL used for resolving relative module imports.
   nsCOMPtr<nsIURI> mBaseURL;
@@ -64,10 +83,6 @@ public:
   // finishes.
   RefPtr<ScriptLoader> mLoader;
 
-  // The importing module, or nullptr for top level module scripts.  Used to
-  // implement the ancestor list checked when fetching module dependencies.
-  RefPtr<ModuleLoadRequest> mParent;
-
   // Set to a module script object after a successful load or nullptr on
   // failure.
   RefPtr<ModuleScript> mModuleScript;
@@ -79,9 +94,13 @@ public:
 
   // Array of imported modules.
   nsTArray<RefPtr<ModuleLoadRequest>> mImports;
+
+  // Set of module URLs visited while fetching the module graph this request is
+  // part of.
+  RefPtr<VisitedURLSet> mVisitedSet;
 };
 
 } // dom namespace
 } // mozilla namespace
 
-#endif // mozilla_dom_ModuleLoadRequest_h
\ No newline at end of file
+#endif // mozilla_dom_ModuleLoadRequest_h
diff --git a/dom/script/ModuleScript.cpp b/dom/script/ModuleScript.cpp
index 28b97a3cb..1bf9d0b0f 100644
--- a/dom/script/ModuleScript.cpp
+++ b/dom/script/ModuleScript.cpp
@@ -26,7 +26,8 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(ModuleScript)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mLoader)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mBaseURL)
   tmp->UnlinkModuleRecord();
-  tmp->mError.setUndefined();
+  tmp->mParseError.setUndefined();
+  tmp->mErrorToRethrow.setUndefined();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(ModuleScript)
@@ -35,7 +36,8 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
 NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(ModuleScript)
   NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mModuleRecord)
-  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mError)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mParseError)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mErrorToRethrow)
 NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(ModuleScript)
@@ -48,7 +50,8 @@ ModuleScript::ModuleScript(ScriptLoader *aLoader, nsIURI* aBaseURL)
   MOZ_ASSERT(mLoader);
   MOZ_ASSERT(mBaseURL);
   MOZ_ASSERT(!mModuleRecord);
-  MOZ_ASSERT(mError.isUndefined());
+  MOZ_ASSERT(!HasParseError());
+  MOZ_ASSERT(!HasErrorToRethrow());
 }
 
 void
@@ -74,7 +77,8 @@ void
 ModuleScript::SetModuleRecord(JS::Handle<JSObject*> aModuleRecord)
 {
   MOZ_ASSERT(!mModuleRecord);
-  MOZ_ASSERT(mError.isUndefined());
+  MOZ_ASSERT(!HasParseError());
+  MOZ_ASSERT(!HasErrorToRethrow());
 
   mModuleRecord = aModuleRecord;
 
@@ -85,37 +89,24 @@ ModuleScript::SetModuleRecord(JS::Handle<JSObject*> aModuleRecord)
 }
 
 void
-ModuleScript::SetPreInstantiationError(const JS::Value& aError)
+ModuleScript::SetParseError(const JS::Value& aError)
 {
   MOZ_ASSERT(!aError.isUndefined());
+  MOZ_ASSERT(!HasParseError());
+  MOZ_ASSERT(!HasErrorToRethrow());
 
   UnlinkModuleRecord();
-  mError = aError;
-
+  mParseError = aError;
   HoldJSObjects(this);
 }
 
-bool
-ModuleScript::IsErrored() const
+void
+ModuleScript::SetErrorToRethrow(const JS::Value& aError)
 {
-  if (!mModuleRecord) {
-    MOZ_ASSERT(!mError.isUndefined());
-    return true;
-  }
+  MOZ_ASSERT(!aError.isUndefined());
+  MOZ_ASSERT(!HasErrorToRethrow());
 
-  return JS::IsModuleErrored(mModuleRecord);
-}
-
-JS::Value
-ModuleScript::Error() const
-{
-  MOZ_ASSERT(IsErrored());
-
-  if (!mModuleRecord) {
-    return mError;
-  }
-
-  return JS::GetModuleError(mModuleRecord);
+  mErrorToRethrow = aError;
 }
 
 } // dom namespace
diff --git a/dom/script/ModuleScript.h b/dom/script/ModuleScript.h
index 571359859..f765aa0fa 100644
--- a/dom/script/ModuleScript.h
+++ b/dom/script/ModuleScript.h
@@ -23,7 +23,8 @@ class ModuleScript final : public nsISupports
   RefPtr<ScriptLoader> mLoader;
   nsCOMPtr<nsIURI> mBaseURL;
   JS::Heap<JSObject*> mModuleRecord;
-  JS::Heap<JS::Value> mError;
+  JS::Heap<JS::Value> mParseError;
+  JS::Heap<JS::Value> mErrorToRethrow;
 
   ~ModuleScript();
 
@@ -35,14 +36,17 @@ public:
                nsIURI* aBaseURL);
 
   void SetModuleRecord(JS::Handle<JSObject*> aModuleRecord);
-  void SetPreInstantiationError(const JS::Value& aError);
+  void SetParseError(const JS::Value& aError);
+  void SetErrorToRethrow(const JS::Value& aError);
 
   ScriptLoader* Loader() const { return mLoader; }
   JSObject* ModuleRecord() const { return mModuleRecord; }
   nsIURI* BaseURL() const { return mBaseURL; }
 
-  bool IsErrored() const;
-  JS::Value Error() const;
+  JS::Value ParseError() const { return mParseError; }
+  JS::Value ErrorToRethrow() const { return mErrorToRethrow; }
+  bool HasParseError() const { return !mParseError.isUndefined(); }
+  bool HasErrorToRethrow() const { return !mErrorToRethrow.isUndefined(); }
 
   void UnlinkModuleRecord();
 };
diff --git a/dom/script/ScriptElement.cpp b/dom/script/ScriptElement.cpp
index 0cb17dcb0..eb20dbf32 100644
--- a/dom/script/ScriptElement.cpp
+++ b/dom/script/ScriptElement.cpp
@@ -21,11 +21,11 @@ using namespace mozilla::dom;
 NS_IMETHODIMP
 ScriptElement::ScriptAvailable(nsresult aResult,
                                nsIScriptElement *aElement,
-                               bool aIsInline,
+                               bool aIsInlineClassicScript,
                                nsIURI *aURI,
                                int32_t aLineNo)
 {
-  if (!aIsInline && NS_FAILED(aResult)) {
+  if (!aIsInlineClassicScript && NS_FAILED(aResult)) {
     nsCOMPtr<nsIParser> parser = do_QueryReferent(mCreatorParser);
     if (parser) {
       parser->PushDefinedInsertionPoint();
@@ -128,11 +128,11 @@ ScriptElement::MaybeProcessScript()
     return false;
   }
 
-  FreezeUriAsyncDefer();
+  nsIDocument* ownerDoc = cont->OwnerDoc();
+  FreezeExecutionAttrs(ownerDoc);
 
   mAlreadyStarted = true;
 
-  nsIDocument* ownerDoc = cont->OwnerDoc();
   nsCOMPtr<nsIParser> parser = ((nsIScriptElement*) this)->GetCreatorParser();
   if (parser) {
     nsCOMPtr<nsIContentSink> sink = parser->GetContentSink();
diff --git a/dom/script/ScriptLoader.cpp b/dom/script/ScriptLoader.cpp
index a53098974..989301b91 100644
--- a/dom/script/ScriptLoader.cpp
+++ b/dom/script/ScriptLoader.cpp
@@ -140,6 +140,18 @@ ScriptLoadRequest::AsModuleRequest()
   return static_cast<ModuleLoadRequest*>(this);
 }
 
+void
+ScriptLoadRequest::SetScriptMode(bool aDeferAttr, bool aAsyncAttr)
+{
+  if (aAsyncAttr) {
+    mScriptMode = ScriptMode::eAsync;
+  } else if (aDeferAttr || IsModuleRequest()) {
+    mScriptMode = ScriptMode::eDeferred;
+  } else {
+    mScriptMode = ScriptMode::eBlocking;
+  }
+}
+
 //////////////////////////////////////////////////////////////
 
 // ScriptLoadRequestList
@@ -299,8 +311,12 @@ ScriptLoader::~ScriptLoader()
 // <script for=... event=...> element.
 
 static bool
-IsScriptEventHandler(nsIContent* aScriptElement)
+IsScriptEventHandler(ScriptKind kind, nsIContent* aScriptElement)
 {
+  if (kind != ScriptKind::Classic) {
+    return false;
+  }
+
   if (!aScriptElement->IsHTMLElement()) {
     return false;
   }
@@ -375,25 +391,12 @@ ScriptLoader::CheckContentPolicy(nsIDocument* aDocument,
 }
 
 bool
-ScriptLoader::ModuleScriptsEnabled()
-{
-  static bool sEnabledForContent = false;
-  static bool sCachedPref = false;
-  if (!sCachedPref) {
-    sCachedPref = true;
-    Preferences::AddBoolVarCache(&sEnabledForContent, "dom.moduleScripts.enabled", false);
-  }
-
-  return nsContentUtils::IsChromeDoc(mDocument) || sEnabledForContent;
-}
-
-bool
-ScriptLoader::ModuleMapContainsModule(ModuleLoadRequest *aRequest) const
+ScriptLoader::ModuleMapContainsURL(nsIURI* aURL) const
 {
   // Returns whether we have fetched, or are currently fetching, a module script
-  // for the request's URL.
-  return mFetchingModules.Contains(aRequest->mURI) ||
-         mFetchedModules.Contains(aRequest->mURI);
+  // for a URL.
+  return mFetchingModules.Contains(aURL) ||
+         mFetchedModules.Contains(aURL);
 }
 
 bool
@@ -410,7 +413,7 @@ ScriptLoader::SetModuleFetchStarted(ModuleLoadRequest *aRequest)
   // Update the module map to indicate that a module is currently being fetched.
 
   MOZ_ASSERT(aRequest->IsLoading());
-  MOZ_ASSERT(!ModuleMapContainsModule(aRequest));
+  MOZ_ASSERT(!ModuleMapContainsURL(aRequest->mURI));
   mFetchingModules.Put(aRequest->mURI, nullptr);
 }
 
@@ -443,21 +446,21 @@ ScriptLoader::SetModuleFetchFinishedAndResumeWaitingRequests(ModuleLoadRequest *
 }
 
 RefPtr<GenericPromise>
-ScriptLoader::WaitForModuleFetch(ModuleLoadRequest *aRequest)
+ScriptLoader::WaitForModuleFetch(nsIURI* aURL)
 {
-  MOZ_ASSERT(ModuleMapContainsModule(aRequest));
+  MOZ_ASSERT(ModuleMapContainsURL(aURL));
 
   RefPtr<GenericPromise::Private> promise;
-  if (mFetchingModules.Get(aRequest->mURI, getter_AddRefs(promise))) {
+  if (mFetchingModules.Get(aURL, getter_AddRefs(promise))) {
     if (!promise) {
       promise = new GenericPromise::Private(__func__);
-      mFetchingModules.Put(aRequest->mURI, promise);
+      mFetchingModules.Put(aURL, promise);
     }
     return promise;
   }
 
   RefPtr<ModuleScript> ms;
-  MOZ_ALWAYS_TRUE(mFetchedModules.Get(aRequest->mURI, getter_AddRefs(ms)));
+  MOZ_ALWAYS_TRUE(mFetchedModules.Get(aURL, getter_AddRefs(ms)));
   if (!ms) {
     return GenericPromise::CreateAndReject(NS_ERROR_FAILURE, __func__);
   }
@@ -482,8 +485,6 @@ ScriptLoader::ProcessFetchedModuleSource(ModuleLoadRequest* aRequest)
   nsresult rv = CreateModuleScript(aRequest);
   MOZ_ASSERT(NS_FAILED(rv) == !aRequest->mModuleScript);
 
-  SetModuleFetchFinishedAndResumeWaitingRequests(aRequest, rv);
-
   free(aRequest->mScriptTextBuf);
   aRequest->mScriptTextBuf = nullptr;
   aRequest->mScriptTextLength = 0;
@@ -493,7 +494,11 @@ ScriptLoader::ProcessFetchedModuleSource(ModuleLoadRequest* aRequest)
     return rv;
   }
 
-  if (!aRequest->mModuleScript->IsErrored()) {
+  if (!aRequest->mIsInline) {
+    SetModuleFetchFinishedAndResumeWaitingRequests(aRequest, rv);
+  }
+
+  if (!aRequest->mModuleScript->HasParseError()) {
     StartFetchingModuleDependencies(aRequest);
   }
 
@@ -501,7 +506,7 @@ ScriptLoader::ProcessFetchedModuleSource(ModuleLoadRequest* aRequest)
 }
 
 static nsresult
-ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI>& aUrls);
+ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI>* aUrlsOut);
 
 nsresult
 ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
@@ -528,7 +533,6 @@ ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
   nsresult rv;
   {
     // Update our current script.
-    AutoCurrentScriptUpdater scriptUpdater(this, aRequest->mElement);
     Maybe<AutoCurrentScriptUpdater> masterScriptUpdater;
     nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
     if (master != mDocument) {
@@ -568,7 +572,7 @@ ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
         return NS_ERROR_FAILURE;
       }
 
-      moduleScript->SetPreInstantiationError(error);
+      moduleScript->SetParseError(error);
       aRequest->ModuleErrored();
       return NS_OK;
     }
@@ -577,11 +581,8 @@ ScriptLoader::CreateModuleScript(ModuleLoadRequest* aRequest)
 
     // Validate requested modules and treat failure to resolve module specifiers
     // the same as a parse error.
-    nsCOMArray<nsIURI> urls;
-    rv = ResolveRequestedModules(aRequest, urls);
+    rv = ResolveRequestedModules(aRequest, nullptr);
     if (NS_FAILED(rv)) {
-      // ResolveRequestedModules sets pre-instanitation error on failure.
-      MOZ_ASSERT(moduleScript->IsErrored());
       aRequest->ModuleErrored();
       return NS_OK;
     }
@@ -627,7 +628,7 @@ HandleResolveFailure(JSContext* aCx, ModuleScript* aScript,
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
-  aScript->SetPreInstantiationError(error);
+  aScript->SetParseError(error);
   return NS_OK;
 }
 
@@ -667,33 +668,7 @@ ResolveModuleSpecifier(ModuleScript* aScript,
 }
 
 static nsresult
-RequestedModuleIsInAncestorList(ModuleLoadRequest* aRequest, nsIURI* aURL, bool* aResult)
-{
-  const size_t ImportDepthLimit = 100;
-
-  *aResult = false;
-  size_t depth = 0;
-  while (aRequest) {
-    if (depth++ == ImportDepthLimit) {
-      return NS_ERROR_FAILURE;
-    }
-
-    bool equal;
-    nsresult rv = aURL->Equals(aRequest->mURI, &equal);
-    NS_ENSURE_SUCCESS(rv, rv);
-    if (equal) {
-      *aResult = true;
-      return NS_OK;
-    }
-
-    aRequest = aRequest->mParent;
-  }
-
-  return NS_OK;
-}
-
-static nsresult
-ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI> &aUrls)
+ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI>* aUrlsOut)
 {
   ModuleScript* ms = aRequest->mModuleScript;
 
@@ -723,7 +698,6 @@ ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI> &aUrls)
     }
 
     // Let url be the result of resolving a module specifier given module script and requested.
-    ModuleScript* ms = aRequest->mModuleScript;
     nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(ms, specifier);
     if (!uri) {
       nsresult rv = HandleResolveFailure(cx, ms, specifier);
@@ -731,11 +705,8 @@ ResolveRequestedModules(ModuleLoadRequest* aRequest, nsCOMArray<nsIURI> &aUrls)
       return NS_ERROR_FAILURE;
     }
 
-    bool isAncestor;
-    nsresult rv = RequestedModuleIsInAncestorList(aRequest, uri, &isAncestor);
-    NS_ENSURE_SUCCESS(rv, rv);
-    if (!isAncestor) {
-      aUrls.AppendElement(uri.forget());
+    if (aUrlsOut) {
+      aUrlsOut->AppendElement(uri.forget());
     }
   }
 
@@ -746,20 +717,36 @@ void
 ScriptLoader::StartFetchingModuleDependencies(ModuleLoadRequest* aRequest)
 {
   MOZ_ASSERT(aRequest->mModuleScript);
-  MOZ_ASSERT(!aRequest->mModuleScript->IsErrored());
+  MOZ_ASSERT(!aRequest->mModuleScript->HasParseError());
   MOZ_ASSERT(!aRequest->IsReadyToRun());
 
+  auto visitedSet = aRequest->mVisitedSet;
+  MOZ_ASSERT(visitedSet->Contains(aRequest->mURI));
+
   aRequest->mProgress = ModuleLoadRequest::Progress::FetchingImports;
 
   nsCOMArray<nsIURI> urls;
-  nsresult rv = ResolveRequestedModules(aRequest, urls);
+  nsresult rv = ResolveRequestedModules(aRequest, &urls);
   if (NS_FAILED(rv)) {
     aRequest->ModuleErrored();
     return;
   }
 
-  if (urls.Length() == 0) {
-    // There are no descendents to load so this request is ready.
+  // Remove already visited URLs from the list. Put unvisited URLs into the
+  // visited set.
+  int32_t i = 0;
+  while (i < urls.Count()) {
+    nsIURI* url = urls[i];
+    if (visitedSet->Contains(url)) {
+      urls.RemoveObjectAt(i);
+    } else {
+      visitedSet->PutEntry(url);
+      i++;
+    }
+  }
+
+  if (urls.Count() == 0) {
+    // There are no descendants to load so this request is ready.
     aRequest->DependenciesLoaded();
     return;
   }
@@ -782,20 +769,14 @@ ScriptLoader::StartFetchingModuleDependencies(ModuleLoadRequest* aRequest)
 }
 
 RefPtr<GenericPromise>
-ScriptLoader::StartFetchingModuleAndDependencies(ModuleLoadRequest* aRequest,
+ScriptLoader::StartFetchingModuleAndDependencies(ModuleLoadRequest* aParent,
                                                  nsIURI* aURI)
 {
   MOZ_ASSERT(aURI);
 
-  RefPtr<ModuleLoadRequest> childRequest =
-    new ModuleLoadRequest(aRequest->mElement, aRequest->mJSVersion,
-                          aRequest->mCORSMode, aRequest->mIntegrity, this);
+  RefPtr<ModuleLoadRequest> childRequest = new ModuleLoadRequest(aURI, aParent);
 
-  childRequest->mIsTopLevel = false;
-  childRequest->mURI = aURI;
-  childRequest->mIsInline = false;
-  childRequest->mReferrerPolicy = aRequest->mReferrerPolicy;
-  childRequest->mParent = aRequest;
+  aParent->mImports.AppendElement(childRequest);
 
   RefPtr<GenericPromise> ready = childRequest->mReady.Ensure(__func__);
 
@@ -806,29 +787,24 @@ ScriptLoader::StartFetchingModuleAndDependencies(ModuleLoadRequest* aRequest,
     return ready;
   }
 
-  aRequest->mImports.AppendElement(childRequest);
   return ready;
 }
 
 // 8.1.3.8.1 HostResolveImportedModule(referencingModule, specifier)
-bool
-HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
+JSObject*
+HostResolveImportedModule(JSContext* aCx, JS::Handle<JSObject*> aModule,
+                          JS::Handle<JSString*> aSpecifier)
 {
-  MOZ_ASSERT(argc == 2);
-  JS::CallArgs args = JS::CallArgsFromVp(argc, vp);
-  JS::Rooted<JSObject*> module(aCx, &args[0].toObject());
-  JS::Rooted<JSString*> specifier(aCx, args[1].toString());
-
   // Let referencing module script be referencingModule.[[HostDefined]].
-  JS::Value value = JS::GetModuleHostDefinedField(module);
+  JS::Value value = JS::GetModuleHostDefinedField(aModule);
   auto script = static_cast<ModuleScript*>(value.toPrivate());
-  MOZ_ASSERT(script->ModuleRecord() == module);
+  MOZ_ASSERT(script->ModuleRecord() == aModule);
 
   // Let url be the result of resolving a module specifier given referencing
   // module script and specifier.
   nsAutoJSString string;
-  if (!string.init(aCx, specifier)) {
-    return false;
+  if (!string.init(aCx, aSpecifier)) {
+    return nullptr;
   }
 
   nsCOMPtr<nsIURI> uri = ResolveModuleSpecifier(script, string);
@@ -843,62 +819,79 @@ HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp)
   ModuleScript* ms = script->Loader()->GetFetchedModule(uri);
   MOZ_ASSERT(ms, "Resolved module not found in module map");
 
-  MOZ_ASSERT(!ms->IsErrored());
+  MOZ_ASSERT(!ms->HasParseError());
+  MOZ_ASSERT(ms->ModuleRecord());
 
-  *vp = JS::ObjectValue(*ms->ModuleRecord());
-  return true;
+  return ms->ModuleRecord();
 }
 
-static nsresult
+static void
 EnsureModuleResolveHook(JSContext* aCx)
 {
-  if (JS::GetModuleResolveHook(aCx)) {
-    return NS_OK;
+  JSRuntime* rt = JS_GetRuntime(aCx);
+  if (JS::GetModuleResolveHook(rt)) {
+    return;
   }
 
-  JS::Rooted<JSFunction*> func(aCx);
-  func = JS_NewFunction(aCx, HostResolveImportedModule, 2, 0,
-                        "HostResolveImportedModule");
-  if (!func) {
-    return NS_ERROR_FAILURE;
-  }
-
-  JS::SetModuleResolveHook(aCx, func);
-  return NS_OK;
+  JS::SetModuleResolveHook(rt, HostResolveImportedModule);
 }
 
 void
 ScriptLoader::CheckModuleDependenciesLoaded(ModuleLoadRequest* aRequest)
 {
   RefPtr<ModuleScript> moduleScript = aRequest->mModuleScript;
-  if (moduleScript && !moduleScript->IsErrored()) {
-    for (auto childRequest : aRequest->mImports) {
-      ModuleScript* childScript = childRequest->mModuleScript;
-      if (!childScript) {
-        // Load error
-        aRequest->mModuleScript = nullptr;
-        return;
-      } else if (childScript->IsErrored()) {
-        // Script error
-        moduleScript->SetPreInstantiationError(childScript->Error());
-        return;
-      }
+  if (!moduleScript || moduleScript->HasParseError()) {
+    return;
+  }
+
+  for (auto childRequest : aRequest->mImports) {
+    ModuleScript* childScript = childRequest->mModuleScript;
+    if (!childScript) {
+      aRequest->mModuleScript = nullptr;
+      // Load error on script load request; bail.
+      return;
     }
   }
 }
 
+class ScriptRequestProcessor : public Runnable
+{
+private:
+  RefPtr<ScriptLoader> mLoader;
+  RefPtr<ScriptLoadRequest> mRequest;
+public:
+  ScriptRequestProcessor(ScriptLoader* aLoader,
+                         ScriptLoadRequest* aRequest)
+    : mLoader(aLoader)
+    , mRequest(aRequest)
+  {}
+  NS_IMETHOD Run() override
+  {
+    return mLoader->ProcessRequest(mRequest);
+  }
+};
+
 void
 ScriptLoader::ProcessLoadedModuleTree(ModuleLoadRequest* aRequest)
 {
   if (aRequest->IsTopLevel()) {
     ModuleScript* moduleScript = aRequest->mModuleScript;
-    if (moduleScript && !moduleScript->IsErrored()) {
+    if (moduleScript && !moduleScript->HasErrorToRethrow()) {
       if (!InstantiateModuleTree(aRequest)) {
         aRequest->mModuleScript = nullptr;
       }
     }
-    MaybeMoveToLoadedList(aRequest);
-    ProcessPendingRequests();
+
+    if (aRequest->mIsInline &&
+        aRequest->mElement->GetParserCreated() == NOT_FROM_PARSER)
+    {
+      MOZ_ASSERT(!aRequest->isInList());
+      nsContentUtils::AddScriptRunner(
+        new ScriptRequestProcessor(this, aRequest));
+    } else {
+      MaybeMoveToLoadedList(aRequest);
+      ProcessPendingRequests();
+    }
   }
 
   if (aRequest->mWasCompiledOMT) {
@@ -906,6 +899,28 @@ ScriptLoader::ProcessLoadedModuleTree(ModuleLoadRequest* aRequest)
   }
 }
 
+JS::Value
+ScriptLoader::FindFirstParseError(ModuleLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest);
+
+  ModuleScript* moduleScript = aRequest->mModuleScript;
+  MOZ_ASSERT(moduleScript);
+
+  if (moduleScript->HasParseError()) {
+    return moduleScript->ParseError();
+  }
+
+  for (ModuleLoadRequest* childRequest : aRequest->mImports) {
+    JS::Value error = FindFirstParseError(childRequest);
+    if (!error.isUndefined()) {
+      return error;
+    }
+  }
+
+  return JS::UndefinedValue();
+}
+
 bool
 ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
 {
@@ -916,6 +931,14 @@ ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
 
   ModuleScript* moduleScript = aRequest->mModuleScript;
   MOZ_ASSERT(moduleScript);
+
+  JS::Value parseError = FindFirstParseError(aRequest);
+  if (!parseError.isUndefined()) {
+    // Parse error found in the requested script
+    moduleScript->SetErrorToRethrow(parseError);
+    return true;
+  }
+
   MOZ_ASSERT(moduleScript->ModuleRecord());
 
   nsAutoMicroTask mt;
@@ -924,8 +947,7 @@ ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
     return false;
   }
 
-  nsresult rv = EnsureModuleResolveHook(jsapi.cx());
-  NS_ENSURE_SUCCESS(rv, false);
+  EnsureModuleResolveHook(jsapi.cx());
 
   JS::Rooted<JSObject*> module(jsapi.cx(), moduleScript->ModuleRecord());
   bool ok = NS_SUCCEEDED(nsJSUtils::ModuleInstantiate(jsapi.cx(), module));
@@ -937,7 +959,7 @@ ScriptLoader::InstantiateModuleTree(ModuleLoadRequest* aRequest)
       return false;
     }
     MOZ_ASSERT(!exception.isUndefined());
-    // Ignore the exception. It will be recorded in the module record.
+    moduleScript->SetErrorToRethrow(exception);
   }
 
   return true;
@@ -959,8 +981,8 @@ ScriptLoader::StartLoad(ScriptLoadRequest *aRequest, const nsAString &aType,
     // Check whether the module has been fetched or is currently being fetched,
     // and if so wait for it.
     ModuleLoadRequest* request = aRequest->AsModuleRequest();
-    if (ModuleMapContainsModule(request)) {
-      WaitForModuleFetch(request)
+    if (ModuleMapContainsURL(request->mURI)) {
+      WaitForModuleFetch(request->mURI)
         ->Then(AbstractThread::GetCurrent(), __func__, request,
                &ModuleLoadRequest::ModuleLoaded,
                &ModuleLoadRequest::LoadFailed);
@@ -1026,16 +1048,14 @@ ScriptLoader::StartLoad(ScriptLoadRequest *aRequest, const nsAString &aType,
 
   NS_ENSURE_SUCCESS(rv, rv);
 
-  nsIScriptElement *script = aRequest->mElement;
   nsCOMPtr<nsIClassOfService> cos(do_QueryInterface(channel));
 
   if (cos) {
-    if (aScriptFromHead &&
-        !(script && (script->GetScriptAsync() || script->GetScriptDeferred()))) {
+    if (aScriptFromHead && aRequest->IsBlockingScript()) {
       // synchronous head scripts block lading of most other non js/css
       // content such as images
       cos->AddClassFlags(nsIClassOfService::Leader);
-    } else if (!(script && script->GetScriptDeferred())) {
+    } else if (!aRequest->IsDeferredScript()) {
       // other scripts are neither blocked nor prioritized unless marked deferred
       cos->AddClassFlags(nsIClassOfService::Unblocked);
     }
@@ -1047,7 +1067,7 @@ ScriptLoader::StartLoad(ScriptLoadRequest *aRequest, const nsAString &aType,
     httpChannel->SetRequestHeader(NS_LITERAL_CSTRING("Accept"),
                                   NS_LITERAL_CSTRING("*/*"),
                                   false);
-    httpChannel->SetReferrerWithPolicy(mDocument->GetDocumentURI(),
+    httpChannel->SetReferrerWithPolicy(aRequest->mReferrer,
                                        aRequest->mReferrerPolicy);
 
     nsCOMPtr<nsIHttpChannelInternal> internalChannel(do_QueryInterface(httpChannel));
@@ -1095,23 +1115,6 @@ ScriptLoader::PreloadURIComparator::Equals(const PreloadInfo &aPi,
          same;
 }
 
-class ScriptRequestProcessor : public Runnable
-{
-private:
-  RefPtr<ScriptLoader> mLoader;
-  RefPtr<ScriptLoadRequest> mRequest;
-public:
-  ScriptRequestProcessor(ScriptLoader* aLoader,
-                         ScriptLoadRequest* aRequest)
-    : mLoader(aLoader)
-    , mRequest(aRequest)
-  {}
-  NS_IMETHOD Run() override
-  {
-    return mLoader->ProcessRequest(mRequest);
-  }
-};
-
 static inline bool
 ParseTypeAttribute(const nsAString& aType, JSVersion* aVersion)
 {
@@ -1176,17 +1179,24 @@ CSPAllowsInlineScript(nsIScriptElement *aElement, nsIDocument *aDocument)
 
 ScriptLoadRequest*
 ScriptLoader::CreateLoadRequest(ScriptKind aKind,
+                                nsIURI* aURI,
                                 nsIScriptElement* aElement,
                                 uint32_t aVersion, CORSMode aCORSMode,
-                                const SRIMetadata &aIntegrity)
+                                const SRIMetadata& aIntegrity,
+                                mozilla::net::ReferrerPolicy aReferrerPolicy)
 {
+  nsIURI* referrer = mDocument->GetDocumentURI();
+
   if (aKind == ScriptKind::Classic) {
-    return new ScriptLoadRequest(aKind, aElement, aVersion, aCORSMode,
-                                 aIntegrity);
+    return new ScriptLoadRequest(aKind, aURI, aElement,
+                                 aVersion, aCORSMode,
+                                 aIntegrity,
+                                 referrer, aReferrerPolicy);
   }
 
   MOZ_ASSERT(aKind == ScriptKind::Module);
-  return new ModuleLoadRequest(aElement, aVersion, aCORSMode, aIntegrity, this);
+  return new ModuleLoadRequest(aURI, aElement, aVersion, aCORSMode,
+                               aIntegrity, referrer, aReferrerPolicy, this);
 }
 
 bool
@@ -1204,35 +1214,36 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
 
   nsCOMPtr<nsIContent> scriptContent = do_QueryInterface(aElement);
 
+  nsAutoString type;
+  bool hasType = aElement->GetScriptType(type);
+
+  ScriptKind scriptKind = aElement->GetScriptIsModule() ?
+                          ScriptKind::Module :
+                          ScriptKind::Classic;
+
   // Step 13. Check that the script is not an eventhandler
-  if (IsScriptEventHandler(scriptContent)) {
+  if (IsScriptEventHandler(scriptKind, scriptContent)) {
     return false;
   }
 
   JSVersion version = JSVERSION_DEFAULT;
 
-  // Check the type attribute to determine language and version.
-  // If type exists, it trumps the deprecated 'language='
-  nsAutoString type;
-  bool hasType = aElement->GetScriptType(type);
-
-  ScriptKind scriptKind = ScriptKind::Classic;
-  if (!type.IsEmpty()) {
-    if (ModuleScriptsEnabled() && type.LowerCaseEqualsASCII("module")) {
-      scriptKind = ScriptKind::Module;
-    } else {
+  // For classic scripts, check the type attribute to determine language and
+  // version. If type exists, it trumps the deprecated 'language='
+  if (scriptKind == ScriptKind::Classic) {
+    if (!type.IsEmpty()) {
       NS_ENSURE_TRUE(ParseTypeAttribute(type, &version), false);
-    }
-  } else if (!hasType) {
-    // no 'type=' element
-    // "language" is a deprecated attribute of HTML, so we check it only for
-    // HTML script elements.
-    if (scriptContent->IsHTMLElement()) {
-      nsAutoString language;
-      scriptContent->GetAttr(kNameSpaceID_None, nsGkAtoms::language, language);
-      if (!language.IsEmpty()) {
-        if (!nsContentUtils::IsJavaScriptLanguage(language)) {
-          return false;
+    } else if (!hasType) {
+      // no 'type=' element
+      // "language" is a deprecated attribute of HTML, so we check it only for
+      // HTML script elements.
+      if (scriptContent->IsHTMLElement()) {
+        nsAutoString language;
+        scriptContent->GetAttr(kNameSpaceID_None, nsGkAtoms::language, language);
+        if (!language.IsEmpty()) {
+          if (!nsContentUtils::IsJavaScriptLanguage(language)) {
+            return false;
+          }
         }
       }
     }
@@ -1242,7 +1253,7 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
   // the nomodule attribute will be ignored".
   // "The nomodule attribute must not be specified on module scripts (and will
   // be ignored if it is)."
-  if (ModuleScriptsEnabled() &&
+  if (mDocument->ModuleScriptsEnabled() &&
       scriptKind == ScriptKind::Classic &&
       scriptContent->IsHTMLElement() &&
       scriptContent->HasAttr(kNameSpaceID_None, nsGkAtoms::nomodule)) {
@@ -1252,6 +1263,7 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
   // Step 15. and later in the HTML5 spec
   nsresult rv = NS_OK;
   RefPtr<ScriptLoadRequest> request;
+  mozilla::net::ReferrerPolicy ourRefPolicy = mDocument->GetReferrerPolicy();
   if (aElement->GetScriptExternal()) {
     // external script
     nsCOMPtr<nsIURI> scriptURI = aElement->GetScriptURI();
@@ -1264,7 +1276,6 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
     }
 
     // Double-check that the preload matches what we're asked to load now.
-    mozilla::net::ReferrerPolicy ourRefPolicy = mDocument->GetReferrerPolicy();
     CORSMode ourCORSMode = aElement->GetCORSMode();
     nsTArray<PreloadInfo>::index_type i =
       mPreloads.IndexOf(scriptURI.get(), 0, PreloadURIComparator());
@@ -1297,8 +1308,15 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
       }
     }
 
-    if (!request) {
-      // no usable preload
+    if (request) {
+      // Use a preload request.
+
+      // It's possible these attributes changed since we started the preload, so
+      // update them here.
+      request->SetScriptMode(aElement->GetScriptDeferred(),
+                             aElement->GetScriptAsync());
+    } else {    
+      // No usable preload found.
 
       SRIMetadata sriMetadata;
       {
@@ -1318,13 +1336,14 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
         }
       }
 
-      request = CreateLoadRequest(scriptKind, aElement, version, ourCORSMode,
-                                  sriMetadata);
-      request->mURI = scriptURI;
+      request = CreateLoadRequest(scriptKind, scriptURI, aElement,
+                                  version, ourCORSMode, sriMetadata,
+                                  ourRefPolicy);
       request->mIsInline = false;
-      request->mReferrerPolicy = ourRefPolicy;
+      request->SetScriptMode(aElement->GetScriptDeferred(),
+                             aElement->GetScriptAsync());
 
-      // set aScriptFromHead to false so we don't treat non preloaded scripts as
+      // Set aScriptFromHead to false so we don't treat non-preloaded scripts as
       // blockers for full page load. See bug 792438.
       rv = StartLoad(request, type, false);
       if (NS_FAILED(rv)) {
@@ -1342,18 +1361,15 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
 
     request->mJSVersion = version;
 
-    if (aElement->GetScriptAsync()) {
-      request->mIsAsync = true;
+    if (request->IsAsyncScript()) {
+      AddAsyncRequest(request);
       if (request->IsReadyToRun()) {
-        mLoadedAsyncRequests.AppendElement(request);
         // The script is available already. Run it ASAP when the event
         // loop gets a chance to spin.
 
         // KVKV TODO: Instead of processing immediately, try off-thread-parsing
         // it and only schedule a pending ProcessRequest if that fails.
         ProcessPendingRequestsAsync();
-      } else {
-        mLoadingAsyncRequests.AppendElement(request);
       }
       return false;
     }
@@ -1372,7 +1388,7 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
     }
     // we now have a parser-inserted request that may or may not be still
     // loading
-    if (aElement->GetScriptDeferred() || request->IsModuleRequest()) {
+    if (request->IsDeferredScript()) {
       // We don't want to run this yet.
       // If we come here, the script is a parser-created script and it has
       // the defer attribute but not the async attribute. Since a
@@ -1440,31 +1456,36 @@ ScriptLoader::ProcessScriptElement(nsIScriptElement *aElement)
     return false;
   }
 
-  // Inline scripts ignore ther CORS mode and are always CORS_NONE
-  request = CreateLoadRequest(scriptKind, aElement, version, CORS_NONE,
-                              SRIMetadata()); // SRI doesn't apply
+  // Inline scripts ignore their CORS mode and are always CORS_NONE.
+  request = CreateLoadRequest(scriptKind, mDocument->GetDocumentURI(), aElement,
+                              version, CORS_NONE,
+                              SRIMetadata(), // SRI doesn't apply
+                              ourRefPolicy);
   request->mJSVersion = version;
   request->mIsInline = true;
-  request->mURI = mDocument->GetDocumentURI();
   request->mLineNo = aElement->GetScriptLineNumber();
 
+  // Only the 'async' attribute is heeded on an inline module script and
+  // inline classic scripts ignore both these attributes.
+  MOZ_ASSERT(!aElement->GetScriptDeferred());
+  MOZ_ASSERT_IF(!request->IsModuleRequest(), !aElement->GetScriptAsync());
+  request->SetScriptMode(false, aElement->GetScriptAsync());
+
   if (request->IsModuleRequest()) {
     ModuleLoadRequest* modReq = request->AsModuleRequest();
     modReq->mBaseURL = mDocument->GetDocBaseURI();
-    rv = CreateModuleScript(modReq);
-    MOZ_ASSERT(NS_FAILED(rv) == !modReq->mModuleScript);
-    if (NS_FAILED(rv)) {
-      modReq->LoadFailed();
-      return false;
-    }
+
     if (aElement->GetScriptAsync()) {
-      mLoadingAsyncRequests.AppendElement(request);
+      AddAsyncRequest(modReq);
     } else {
-      AddDeferRequest(request);
+      AddDeferRequest(modReq);
     }
-    if (!modReq->mModuleScript->IsErrored()) {
-      StartFetchingModuleDependencies(modReq);
+
+    nsresult rv = ProcessFetchedModuleSource(modReq);
+    if (NS_FAILED(rv)) {
+      HandleLoadError(modReq, rv);
     }
+
     return false;
   }
   request->mProgress = ScriptLoadRequest::Progress::Ready;
@@ -1943,8 +1964,6 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
   context->SetProcessingScriptTag(true);
   nsresult rv;
   {
-    // Update our current script.
-    AutoCurrentScriptUpdater scriptUpdater(this, aRequest->mElement);
     Maybe<AutoCurrentScriptUpdater> masterScriptUpdater;
     nsCOMPtr<nsIDocument> master = mDocument->MasterDocument();
     if (master != mDocument) {
@@ -1958,17 +1977,19 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
     }
 
     if (aRequest->IsModuleRequest()) {
-      rv = EnsureModuleResolveHook(cx);
-      NS_ENSURE_SUCCESS(rv, rv);
+      // For modules, currentScript is set to null.
+      AutoCurrentScriptUpdater scriptUpdater(this, nullptr);
+
+      EnsureModuleResolveHook(cx);
 
       ModuleLoadRequest* request = aRequest->AsModuleRequest();
       MOZ_ASSERT(request->mModuleScript);
       MOZ_ASSERT(!request->mOffThreadToken);
 
       ModuleScript* moduleScript = request->mModuleScript;
-      if (moduleScript->IsErrored()) {
-        // Module has an error status
-        JS::Rooted<JS::Value> error(cx, moduleScript->Error());
+      if (moduleScript->HasErrorToRethrow()) {
+        // Module has an error status to be rethrown
+        JS::Rooted<JS::Value> error(cx, moduleScript->ErrorToRethrow());
         JS_SetPendingException(cx, error);
         return NS_OK; // An error is reported by AutoEntryScript.
       }
@@ -1983,6 +2004,9 @@ ScriptLoader::EvaluateScript(ScriptLoadRequest* aRequest)
         rv = NS_OK; // An error is reported by AutoEntryScript.
       }
     } else {
+      // Update our current script.
+      AutoCurrentScriptUpdater scriptUpdater(this, aRequest->mElement);
+
       JS::CompileOptions options(cx);
       rv = FillCompileOptionsForRequest(aes, aRequest, global, &options);
 
@@ -2236,19 +2260,41 @@ ScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
                                nsresult aChannelStatus,
                                nsresult aSRIStatus,
                                mozilla::Vector<char16_t> &aString,
-                               mozilla::dom::SRICheckDataVerifier* aSRIDataVerifier)
+                               SRICheckDataVerifier* aSRIDataVerifier)
 {
   ScriptLoadRequest* request = static_cast<ScriptLoadRequest*>(aContext);
   NS_ASSERTION(request, "null request in stream complete handler");
   NS_ENSURE_TRUE(request, NS_ERROR_FAILURE);
 
+  nsresult rv = VerifySRI(request, aLoader, aSRIStatus, aSRIDataVerifier);
+
+  if (NS_SUCCEEDED(rv)) {
+    rv = PrepareLoadedRequest(request, aLoader, aChannelStatus, aString);
+  }
+
+  if (NS_FAILED(rv)) {
+    HandleLoadError(request, rv);
+  }
+
+  // Process our request and/or any pending ones
+  ProcessPendingRequests();
+
+  return NS_OK;
+}
+
+nsresult
+ScriptLoader::VerifySRI(ScriptLoadRequest* aRequest,
+                        nsIIncrementalStreamLoader* aLoader,
+                        nsresult aSRIStatus,
+                        SRICheckDataVerifier* aSRIDataVerifier) const
+{
   nsCOMPtr<nsIRequest> channelRequest;
   aLoader->GetRequest(getter_AddRefs(channelRequest));
   nsCOMPtr<nsIChannel> channel;
   channel = do_QueryInterface(channelRequest);
 
   nsresult rv = NS_OK;
-  if (!request->mIntegrity.IsEmpty() &&
+  if (!aRequest->mIntegrity.IsEmpty() &&
       NS_SUCCEEDED((rv = aSRIStatus))) {
     MOZ_ASSERT(aSRIDataVerifier);
     MOZ_ASSERT(mReporter);
@@ -2257,7 +2303,7 @@ ScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
     if (mDocument && mDocument->GetDocumentURI()) {
       mDocument->GetDocumentURI()->GetAsciiSpec(sourceUri);
     }
-    rv = aSRIDataVerifier->Verify(request->mIntegrity, channel, sourceUri,
+    rv = aSRIDataVerifier->Verify(aRequest->mIntegrity, channel, sourceUri,
                                   mReporter);
     mReporter->FlushConsoleReports(mDocument);
     if (NS_FAILED(rv)) {
@@ -2273,7 +2319,7 @@ ScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
       loadInfo->LoadingPrincipal()->GetCsp(getter_AddRefs(csp));
       nsAutoCString violationURISpec;
       mDocument->GetDocumentURI()->GetAsciiSpec(violationURISpec);
-      uint32_t lineNo = request->mElement ? request->mElement->GetScriptLineNumber() : 0;
+      uint32_t lineNo = aRequest->mElement ? aRequest->mElement->GetScriptLineNumber() : 0;
       csp->LogViolationDetails(
         nsIContentSecurityPolicy::VIOLATION_TYPE_REQUIRE_SRI_FOR_SCRIPT,
         NS_ConvertUTF8toUTF16(violationURISpec),
@@ -2281,78 +2327,79 @@ ScriptLoader::OnStreamComplete(nsIIncrementalStreamLoader* aLoader,
       rv = NS_ERROR_SRI_CORRUPT;
     }
   }
-
-  if (NS_SUCCEEDED(rv)) {
-    rv = PrepareLoadedRequest(request, aLoader, aChannelStatus, aString);
-  }
-
-  if (NS_FAILED(rv)) {
-    /*
-     * Handle script not loading error because source was a tracking URL.
-     * We make a note of this script node by including it in a dedicated
-     * array of blocked tracking nodes under its parent document.
-     */
-    if (rv == NS_ERROR_TRACKING_URI) {
-      nsCOMPtr<nsIContent> cont = do_QueryInterface(request->mElement);
-      mDocument->AddBlockedTrackingNode(cont);
-    }
-
-    if (request->mIsDefer) {
-      MOZ_ASSERT_IF(request->IsModuleRequest(),
-                    request->AsModuleRequest()->IsTopLevel());
-      if (request->isInList()) {
-        RefPtr<ScriptLoadRequest> req = mDeferRequests.Steal(request);
-        FireScriptAvailable(rv, req);
-      }
-    } else if (request->mIsAsync) {
-      MOZ_ASSERT_IF(request->IsModuleRequest(),
-                    request->AsModuleRequest()->IsTopLevel());
-      if (request->isInList()) {
-        RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(request);
-        FireScriptAvailable(rv, req);
-      }
-    } else if (request->mIsNonAsyncScriptInserted) {
-      if (request->isInList()) {
-        RefPtr<ScriptLoadRequest> req =
-          mNonAsyncExternalScriptInsertedRequests.Steal(request);
-        FireScriptAvailable(rv, req);
-      }
-    } else if (request->mIsXSLT) {
-      if (request->isInList()) {
-        RefPtr<ScriptLoadRequest> req = mXSLTRequests.Steal(request);
-        FireScriptAvailable(rv, req);
-      }
-    } else if (request->IsModuleRequest()) {
-      ModuleLoadRequest* modReq = request->AsModuleRequest();
-      MOZ_ASSERT(!modReq->IsTopLevel());
-      MOZ_ASSERT(!modReq->isInList());
-      modReq->Cancel();
-      FireScriptAvailable(rv, request);
-    } else if (mParserBlockingRequest == request) {
-      MOZ_ASSERT(!request->isInList());
-      mParserBlockingRequest = nullptr;
-      UnblockParser(request);
-
-      // Ensure that we treat request->mElement as our current parser-inserted
-      // script while firing onerror on it.
-      MOZ_ASSERT(request->mElement->GetParserCreated());
-      nsCOMPtr<nsIScriptElement> oldParserInsertedScript =
-        mCurrentParserInsertedScript;
-      mCurrentParserInsertedScript = request->mElement;
-      FireScriptAvailable(rv, request);
-      ContinueParserAsync(request);
-      mCurrentParserInsertedScript = oldParserInsertedScript;
-    } else {
-      mPreloads.RemoveElement(request, PreloadRequestComparator());
-    }
-  }
-
-  // Process our request and/or any pending ones
-  ProcessPendingRequests();
-
-  return NS_OK;
+  
+  return rv;
 }
 
+void
+ScriptLoader::HandleLoadError(ScriptLoadRequest *aRequest, nsresult aResult) {
+  /*
+   * Handle script not loading error because source was a tracking URL.
+   * We make a note of this script node by including it in a dedicated
+   * array of blocked tracking nodes under its parent document.
+   */
+  if (aResult == NS_ERROR_TRACKING_URI) {
+    nsCOMPtr<nsIContent> cont = do_QueryInterface(aRequest->mElement);
+    mDocument->AddBlockedTrackingNode(cont);
+  }
+
+  if (aRequest->IsModuleRequest() && !aRequest->mIsInline) {
+    auto request = aRequest->AsModuleRequest();
+    SetModuleFetchFinishedAndResumeWaitingRequests(request, aResult);
+  }
+
+  if (aRequest->mInDeferList) {
+    MOZ_ASSERT_IF(aRequest->IsModuleRequest(),
+                  aRequest->AsModuleRequest()->IsTopLevel());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mDeferRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->mInAsyncList) {
+    MOZ_ASSERT_IF(aRequest->IsModuleRequest(),
+                  aRequest->AsModuleRequest()->IsTopLevel());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->mIsNonAsyncScriptInserted) {
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req =
+        mNonAsyncExternalScriptInsertedRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->mIsXSLT) {
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mXSLTRequests.Steal(aRequest);
+      FireScriptAvailable(aResult, req);
+    }
+  } else if (aRequest->IsModuleRequest()) {
+    ModuleLoadRequest* modReq = aRequest->AsModuleRequest();
+    MOZ_ASSERT(!modReq->IsTopLevel());
+    MOZ_ASSERT(!modReq->isInList());
+    modReq->Cancel();
+    // A single error is fired for the top level module, so don't use
+    // FireScriptAvailable here.
+  } else if (mParserBlockingRequest == aRequest) {
+    MOZ_ASSERT(!aRequest->isInList());
+    mParserBlockingRequest = nullptr;
+    UnblockParser(aRequest);
+
+    // Ensure that we treat request->mElement as our current parser-inserted
+    // script while firing onerror on it.
+    MOZ_ASSERT(aRequest->mElement->GetParserCreated());
+    nsCOMPtr<nsIScriptElement> oldParserInsertedScript =
+      mCurrentParserInsertedScript;
+    mCurrentParserInsertedScript = aRequest->mElement;
+    FireScriptAvailable(aResult, aRequest);
+    ContinueParserAsync(aRequest);
+    mCurrentParserInsertedScript = oldParserInsertedScript;
+  } else {
+    mPreloads.RemoveElement(aRequest, PreloadRequestComparator());
+  }
+}
+
+
 void
 ScriptLoader::UnblockParser(ScriptLoadRequest* aParserBlockingRequest)
 {
@@ -2377,23 +2424,6 @@ ScriptLoader::NumberOfProcessors()
   return mNumberOfProcessors;
 }
 
-void
-ScriptLoader::MaybeMoveToLoadedList(ScriptLoadRequest* aRequest)
-{
-  MOZ_ASSERT(aRequest->IsReadyToRun());
-
-  // If it's async, move it to the loaded list.  aRequest->mIsAsync really
-  // _should_ be in a list, but the consequences if it's not are bad enough we
-  // want to avoid trying to move it if it's not.
-  if (aRequest->mIsAsync) {
-    MOZ_ASSERT(aRequest->isInList());
-    if (aRequest->isInList()) {
-      RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
-      mLoadedAsyncRequests.AppendElement(req);
-    }
-  }
-}
-
 nsresult
 ScriptLoader::PrepareLoadedRequest(ScriptLoadRequest* aRequest,
                                    nsIIncrementalStreamLoader* aLoader,
@@ -2440,10 +2470,10 @@ ScriptLoader::PrepareLoadedRequest(ScriptLoadRequest* aRequest,
   }
 
   nsCOMPtr<nsIChannel> channel = do_QueryInterface(req);
-  // If this load was subject to a CORS check; don't flag it with a
-  // separate origin principal, so that it will treat our document's
-  // principal as the origin principal
-  if (aRequest->mCORSMode == CORS_NONE) {
+  // If this load was subject to a CORS check, don't flag it with a separate
+  // origin principal, so that it will treat our document's principal as the
+  // origin principal.  Module loads always use CORS.
+  if (!aRequest->IsModuleRequest() && aRequest->mCORSMode == CORS_NONE) {
     rv = nsContentUtils::GetSecurityManager()->
       GetChannelResultPrincipal(channel, getter_AddRefs(aRequest->mOriginPrincipal));
     NS_ENSURE_SUCCESS(rv, rv);
@@ -2551,6 +2581,8 @@ ScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
                          const nsAString &aCrossOrigin,
                          const nsAString& aIntegrity,
                          bool aScriptFromHead,
+                         bool aAsync,
+                         bool aDefer,
                          const mozilla::net::ReferrerPolicy aReferrerPolicy)
 {
   NS_ENSURE_TRUE_VOID(mDocument);
@@ -2560,7 +2592,7 @@ ScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
   }
 
   // TODO: Preload module scripts.
-  if (ModuleScriptsEnabled() && aType.LowerCaseEqualsASCII("module")) {
+  if (mDocument->ModuleScriptsEnabled() && aType.LowerCaseEqualsASCII("module")) {
     return;
   }
 
@@ -2577,11 +2609,11 @@ ScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
   }
 
   RefPtr<ScriptLoadRequest> request =
-    CreateLoadRequest(ScriptKind::Classic, nullptr, 0,
-                      Element::StringToCORSMode(aCrossOrigin), sriMetadata);
-  request->mURI = aURI;
+    CreateLoadRequest(ScriptKind::Classic, aURI, nullptr, 0,
+                      Element::StringToCORSMode(aCrossOrigin), sriMetadata,
+                      aReferrerPolicy);
   request->mIsInline = false;
-  request->mReferrerPolicy = aReferrerPolicy;
+  request->SetScriptMode(aDefer, aAsync);
 
   nsresult rv = StartLoad(request, aType, aScriptFromHead);
   if (NS_FAILED(rv)) {
@@ -2596,7 +2628,10 @@ ScriptLoader::PreloadURI(nsIURI *aURI, const nsAString &aCharset,
 void
 ScriptLoader::AddDeferRequest(ScriptLoadRequest* aRequest)
 {
-  aRequest->mIsDefer = true;
+  MOZ_ASSERT(aRequest->IsDeferredScript());
+  MOZ_ASSERT(!aRequest->mInDeferList && !aRequest->mInAsyncList);
+
+  aRequest->mInDeferList = true;
   mDeferRequests.AppendElement(aRequest);
   if (mDeferEnabled && aRequest == mDeferRequests.getFirst() &&
       mDocument && !mBlockingDOMContentLoaded) {
@@ -2606,6 +2641,37 @@ ScriptLoader::AddDeferRequest(ScriptLoadRequest* aRequest)
   }
 }
 
+void
+ScriptLoader::AddAsyncRequest(ScriptLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest->IsAsyncScript());
+  MOZ_ASSERT(!aRequest->mInDeferList && !aRequest->mInAsyncList);
+
+  aRequest->mInAsyncList = true;
+  if (aRequest->IsReadyToRun()) {
+    mLoadedAsyncRequests.AppendElement(aRequest);
+  } else {
+    mLoadingAsyncRequests.AppendElement(aRequest);
+  }
+}
+
+void
+ScriptLoader::MaybeMoveToLoadedList(ScriptLoadRequest* aRequest)
+{
+  MOZ_ASSERT(aRequest->IsReadyToRun());
+
+  // If it's async, move it to the loaded list.  aRequest->mInAsyncList really
+  // _should_ be in a list, but the consequences if it's not are bad enough we
+  // want to avoid trying to move it if it's not.
+  if (aRequest->mInAsyncList) {
+    MOZ_ASSERT(aRequest->isInList());
+    if (aRequest->isInList()) {
+      RefPtr<ScriptLoadRequest> req = mLoadingAsyncRequests.Steal(aRequest);
+      mLoadedAsyncRequests.AppendElement(req);
+    }
+  }
+}
+
 bool
 ScriptLoader::MaybeRemovedDeferRequests()
 {
diff --git a/dom/script/ScriptLoader.h b/dom/script/ScriptLoader.h
index e6b75bf3b..ed1e6acbc 100644
--- a/dom/script/ScriptLoader.h
+++ b/dom/script/ScriptLoader.h
@@ -62,17 +62,21 @@ protected:
 
 public:
   ScriptLoadRequest(ScriptKind aKind,
+                    nsIURI* aURI,
                     nsIScriptElement* aElement,
                     uint32_t aVersion,
                     mozilla::CORSMode aCORSMode,
-                    const mozilla::dom::SRIMetadata &aIntegrity)
+                    const SRIMetadata& aIntegrity,
+                    nsIURI* aReferrer,
+                    mozilla::net::ReferrerPolicy aReferrerPolicy)
     : mKind(aKind),
       mElement(aElement),
       mProgress(Progress::Loading),
+      mScriptMode(ScriptMode::eBlocking),
       mIsInline(true),
       mHasSourceMapURL(false),
-      mIsDefer(false),
-      mIsAsync(false),
+      mInDeferList(false),
+      mInAsyncList(false),
       mIsNonAsyncScriptInserted(false),
       mIsXSLT(false),
       mIsCanceled(false),
@@ -81,10 +85,12 @@ public:
       mScriptTextBuf(nullptr),
       mScriptTextLength(0),
       mJSVersion(aVersion),
+      mURI(aURI),
       mLineNo(1),
       mCORSMode(aCORSMode),
       mIntegrity(aIntegrity),
-      mReferrerPolicy(mozilla::net::RP_Default)
+      mReferrer(aReferrer),
+      mReferrerPolicy(aReferrerPolicy)
   {
   }
 
@@ -100,7 +106,8 @@ public:
 
   void FireScriptAvailable(nsresult aResult)
   {
-    mElement->ScriptAvailable(aResult, mElement, mIsInline, mURI, mLineNo);
+    bool isInlineClassicScript = mIsInline && !IsModuleRequest();
+    mElement->ScriptAvailable(aResult, mElement, isInlineClassicScript, mURI, mLineNo);
   }
   void FireScriptEvaluated(nsresult aResult)
   {
@@ -143,6 +150,29 @@ public:
            (IsReadyToRun() && mWasCompiledOMT);
   }
 
+  enum class ScriptMode : uint8_t {
+    eBlocking,
+    eDeferred,
+    eAsync
+  };
+
+  void SetScriptMode(bool aDeferAttr, bool aAsyncAttr);
+
+  bool IsBlockingScript() const
+  {
+    return mScriptMode == ScriptMode::eBlocking;
+  }
+
+  bool IsDeferredScript() const
+  {
+    return mScriptMode == ScriptMode::eDeferred;
+  }
+
+  bool IsAsyncScript() const
+  {
+    return mScriptMode == ScriptMode::eAsync;
+  }
+
   void MaybeCancelOffThreadScript();
 
   using super::getNext;
@@ -151,10 +181,11 @@ public:
   const ScriptKind mKind;
   nsCOMPtr<nsIScriptElement> mElement;
   Progress mProgress;     // Are we still waiting for a load to complete?
+  ScriptMode mScriptMode; // Whether this script is blocking, deferred or async.
   bool mIsInline;         // Is the script inline or loaded?
   bool mHasSourceMapURL;  // Does the HTTP header have a source map url?
-  bool mIsDefer;          // True if we live in mDeferRequests.
-  bool mIsAsync;          // True if we live in mLoadingAsyncRequests or mLoadedAsyncRequests.
+  bool mInDeferList;      // True if we live in mDeferRequests.
+  bool mInAsyncList;      // True if we live in mLoadingAsyncRequests or mLoadedAsyncRequests.
   bool mIsNonAsyncScriptInserted; // True if we live in mNonAsyncExternalScriptInsertedRequests
   bool mIsXSLT;           // True if we live in mXSLTRequests.
   bool mIsCanceled;       // True if we have been explicitly canceled.
@@ -164,13 +195,14 @@ public:
   char16_t* mScriptTextBuf; // Holds script text for non-inline scripts. Don't
   size_t mScriptTextLength; // use nsString so we can give ownership to jsapi.
   uint32_t mJSVersion;
-  nsCOMPtr<nsIURI> mURI;
+  const nsCOMPtr<nsIURI> mURI;
   nsCOMPtr<nsIPrincipal> mOriginPrincipal;
   nsAutoCString mURL;     // Keep the URI's filename alive during off thread parsing.
   int32_t mLineNo;
   const mozilla::CORSMode mCORSMode;
-  const mozilla::dom::SRIMetadata mIntegrity;
-  mozilla::net::ReferrerPolicy mReferrerPolicy;
+  const SRIMetadata mIntegrity;
+  const nsCOMPtr<nsIURI> mReferrer;
+  const mozilla::net::ReferrerPolicy mReferrerPolicy;
 };
 
 class ScriptLoadRequestList : private mozilla::LinkedList<ScriptLoadRequest>
@@ -452,6 +484,8 @@ public:
                           const nsAString &aCrossOrigin,
                           const nsAString& aIntegrity,
                           bool aScriptFromHead,
+                          bool aAsync,
+                          bool aDefer,
                           const mozilla::net::ReferrerPolicy aReferrerPolicy);
 
   /**
@@ -467,12 +501,13 @@ public:
 private:
   virtual ~ScriptLoader();
 
-  ScriptLoadRequest* CreateLoadRequest(
-    ScriptKind aKind,
-    nsIScriptElement* aElement,
-    uint32_t aVersion,
-    mozilla::CORSMode aCORSMode,
-    const mozilla::dom::SRIMetadata &aIntegrity);
+  ScriptLoadRequest* CreateLoadRequest(ScriptKind aKind,
+                                       nsIURI* aURI,
+                                       nsIScriptElement* aElement,
+                                       uint32_t aVersion,
+                                       mozilla::CORSMode aCORSMode,
+                                       const SRIMetadata& aIntegrity,
+                                       mozilla::net::ReferrerPolicy aReferrerPolicy);
 
   /**
    * Unblocks the creator parser of the parser-blocking scripts.
@@ -500,6 +535,8 @@ private:
   nsresult StartLoad(ScriptLoadRequest *aRequest, const nsAString &aType,
                      bool aScriptFromHead);
 
+  void HandleLoadError(ScriptLoadRequest *aRequest, nsresult aResult);
+
   /**
    * Process any pending requests asynchronously (i.e. off an event) if there
    * are any. Note that this is a no-op if there aren't any currently pending
@@ -534,6 +571,11 @@ private:
     return mEnabled && !mBlockerCount;
   }
 
+  nsresult VerifySRI(ScriptLoadRequest *aRequest,
+                     nsIIncrementalStreamLoader* aLoader,
+                     nsresult aSRIStatus,
+                     SRICheckDataVerifier* aSRIDataVerifier) const;
+
   nsresult AttemptAsyncScriptCompile(ScriptLoadRequest* aRequest);
   nsresult ProcessRequest(ScriptLoadRequest* aRequest);
   nsresult CompileOffThreadOrProcessRequest(ScriptLoadRequest* aRequest);
@@ -556,6 +598,7 @@ private:
                                 mozilla::Vector<char16_t> &aString);
 
   void AddDeferRequest(ScriptLoadRequest* aRequest);
+  void AddAsyncRequest(ScriptLoadRequest* aRequest);
   bool MaybeRemovedDeferRequests();
 
   void MaybeMoveToLoadedList(ScriptLoadRequest* aRequest);
@@ -563,30 +606,30 @@ private:
   JS::SourceBufferHolder GetScriptSource(ScriptLoadRequest* aRequest,
                                          nsAutoString& inlineData);
 
-  bool ModuleScriptsEnabled();
-
   void SetModuleFetchStarted(ModuleLoadRequest *aRequest);
   void SetModuleFetchFinishedAndResumeWaitingRequests(ModuleLoadRequest *aRequest,
                                                       nsresult aResult);
 
   bool IsFetchingModule(ModuleLoadRequest *aRequest) const;
 
-  bool ModuleMapContainsModule(ModuleLoadRequest *aRequest) const;
-  RefPtr<mozilla::GenericPromise> WaitForModuleFetch(ModuleLoadRequest *aRequest);
+  bool ModuleMapContainsURL(nsIURI* aURL) const;
+  RefPtr<mozilla::GenericPromise> WaitForModuleFetch(nsIURI* aURL);
   ModuleScript* GetFetchedModule(nsIURI* aURL) const;
 
-  friend bool
-  HostResolveImportedModule(JSContext* aCx, unsigned argc, JS::Value* vp);
+  friend JSObject*
+  HostResolveImportedModule(JSContext* aCx, JS::Handle<JSObject*> aModule,
+                          JS::Handle<JSString*> aSpecifier);
 
   nsresult CreateModuleScript(ModuleLoadRequest* aRequest);
   nsresult ProcessFetchedModuleSource(ModuleLoadRequest* aRequest);
   void CheckModuleDependenciesLoaded(ModuleLoadRequest* aRequest);
   void ProcessLoadedModuleTree(ModuleLoadRequest* aRequest);
+  JS::Value FindFirstParseError(ModuleLoadRequest* aRequest);
   bool InstantiateModuleTree(ModuleLoadRequest* aRequest);
   void StartFetchingModuleDependencies(ModuleLoadRequest* aRequest);
 
   RefPtr<mozilla::GenericPromise>
-  StartFetchingModuleAndDependencies(ModuleLoadRequest* aRequest, nsIURI* aURI);
+  StartFetchingModuleAndDependencies(ModuleLoadRequest* aParent, nsIURI* aURI);
 
   nsIDocument* mDocument;                   // [WEAK]
   nsCOMArray<nsIScriptLoaderObserver> mObservers;
diff --git a/dom/script/nsIScriptElement.h b/dom/script/nsIScriptElement.h
index 470d51c94..e3e1bc49a 100644
--- a/dom/script/nsIScriptElement.h
+++ b/dom/script/nsIScriptElement.h
@@ -13,6 +13,7 @@
 #include "nsIScriptLoaderObserver.h"
 #include "nsWeakPtr.h"
 #include "nsIParser.h"
+#include "nsIDocument.h"
 #include "nsContentCreatorFunctions.h"
 #include "nsIDOMHTMLScriptElement.h"
 #include "mozilla/CORSMode.h"
@@ -37,6 +38,7 @@ public:
       mForceAsync(aFromParser == mozilla::dom::NOT_FROM_PARSER ||
                   aFromParser == mozilla::dom::FROM_PARSER_FRAGMENT),
       mFrozen(false),
+      mIsModule(false),
       mDefer(false),
       mAsync(false),
       mExternal(false),
@@ -73,11 +75,25 @@ public:
   virtual void GetScriptCharset(nsAString& charset) = 0;
 
   /**
-   * Freezes the return values of GetScriptDeferred(), GetScriptAsync() and
-   * GetScriptURI() so that subsequent modifications to the attributes don't
-   * change execution behavior.
+   * Freezes the return values of the following methods so that subsequent
+   * modifications to the attributes don't change execution behavior:
+   *  - GetScriptIsModule()
+   *  - GetScriptDeferred()
+   *  - GetScriptAsync()
+   *  - GetScriptURI()
+   *  - GetScriptExternal()
    */
-  virtual void FreezeUriAsyncDefer() = 0;
+  virtual void FreezeExecutionAttrs(nsIDocument* aOwnerDoc) = 0;
+
+  /**
+   * Is the script a module script?
+   * Currently only supported by HTML scripts.
+   */
+  bool GetScriptIsModule()
+  {
+    NS_PRECONDITION(mFrozen, "Execution attributes not yet frozen: Not ready for this call!");
+    return mIsModule;
+  }
 
   /**
    * Is the script deferred. Currently only supported by HTML scripts.
@@ -292,6 +308,11 @@ protected:
    */
   bool mFrozen;
 
+  /**
+   * The effective moduleness.
+   */
+  bool mIsModule;
+
   /**
    * The effective deferredness.
    */
diff --git a/dom/script/nsIScriptLoaderObserver.idl b/dom/script/nsIScriptLoaderObserver.idl
index ed7196525..880738360 100644
--- a/dom/script/nsIScriptLoaderObserver.idl
+++ b/dom/script/nsIScriptLoaderObserver.idl
@@ -20,15 +20,16 @@ interface nsIScriptLoaderObserver : nsISupports {
    *        a script. If this is a failure code, script evaluation
    *        will not occur.
    * @param aElement The element being processed.
-   * @param aIsInline Is this an inline script or externally loaded?
+   * @param aIsInline Is this an inline classic script (as opposed to an
+   *        externally loaded classic script or module script)?
    * @param aURI What is the URI of the script (the document URI if
    *        it is inline).
    * @param aLineNo At what line does the script appear (generally 1
    *        if it is a loaded script).
    */
-  void scriptAvailable(in nsresult aResult, 
+  void scriptAvailable(in nsresult aResult,
                        in nsIScriptElement aElement,
-                       in boolean aIsInline,
+                       in boolean aIsInlineClassicScript,
                        in nsIURI aURI,
                        in int32_t aLineNo);
 
@@ -40,7 +41,7 @@ interface nsIScriptLoaderObserver : nsISupports {
    * @param aElement The element being processed.
    * @param aIsInline Is this an inline script or externally loaded?
    */
-  void scriptEvaluated(in nsresult aResult, 
+  void scriptEvaluated(in nsresult aResult,
                        in nsIScriptElement aElement,
                        in boolean aIsInline);
 		       
diff --git a/dom/svg/SVGScriptElement.cpp b/dom/svg/SVGScriptElement.cpp
index 7adce2f46..9a4afb13a 100644
--- a/dom/svg/SVGScriptElement.cpp
+++ b/dom/svg/SVGScriptElement.cpp
@@ -137,7 +137,7 @@ SVGScriptElement::GetScriptCharset(nsAString& charset)
 }
 
 void
-SVGScriptElement::FreezeUriAsyncDefer()
+SVGScriptElement::FreezeExecutionAttrs(nsIDocument* aOwnerDoc)
 {
   if (mFrozen) {
     return;
diff --git a/dom/svg/SVGScriptElement.h b/dom/svg/SVGScriptElement.h
index 79a3de70d..8ee94bf02 100644
--- a/dom/svg/SVGScriptElement.h
+++ b/dom/svg/SVGScriptElement.h
@@ -44,7 +44,7 @@ public:
   virtual bool GetScriptType(nsAString& type) override;
   virtual void GetScriptText(nsAString& text) override;
   virtual void GetScriptCharset(nsAString& charset) override;
-  virtual void FreezeUriAsyncDefer() override;
+  virtual void FreezeExecutionAttrs(nsIDocument* aOwnerDoc) override;
   virtual CORSMode GetCORSMode() const override;
 
   // ScriptElement
diff --git a/dom/xslt/xslt/txMozillaXMLOutput.cpp b/dom/xslt/xslt/txMozillaXMLOutput.cpp
index 704d8ac11..21b3c228f 100644
--- a/dom/xslt/xslt/txMozillaXMLOutput.cpp
+++ b/dom/xslt/xslt/txMozillaXMLOutput.cpp
@@ -955,7 +955,7 @@ NS_IMPL_ISUPPORTS(txTransformNotifier,
 NS_IMETHODIMP
 txTransformNotifier::ScriptAvailable(nsresult aResult, 
                                      nsIScriptElement *aElement, 
-                                     bool aIsInline,
+                                     bool aIsInlineClassicScript,
                                      nsIURI *aURI, 
                                      int32_t aLineNo)
 {
diff --git a/js/public/Class.h b/js/public/Class.h
index 3d73bce44..f4fa9ccaf 100644
--- a/js/public/Class.h
+++ b/js/public/Class.h
@@ -779,7 +779,7 @@ struct JSClass {
 // application.
 #define JSCLASS_GLOBAL_APPLICATION_SLOTS 5
 #define JSCLASS_GLOBAL_SLOT_COUNT                                             \
-    (JSCLASS_GLOBAL_APPLICATION_SLOTS + JSProto_LIMIT * 2 + 46)
+    (JSCLASS_GLOBAL_APPLICATION_SLOTS + JSProto_LIMIT * 2 + 45)
 #define JSCLASS_GLOBAL_FLAGS_WITH_SLOTS(n)                                    \
     (JSCLASS_IS_GLOBAL | JSCLASS_HAS_RESERVED_SLOTS(JSCLASS_GLOBAL_SLOT_COUNT + (n)))
 #define JSCLASS_GLOBAL_FLAGS                                                  \
diff --git a/js/src/builtin/Module.js b/js/src/builtin/Module.js
index 64d62d216..355303d44 100644
--- a/js/src/builtin/Module.js
+++ b/js/src/builtin/Module.js
@@ -67,10 +67,16 @@ function ModuleGetExportedNames(exportStarSet = [])
 
 function ModuleSetStatus(module, newStatus)
 {
-    assert(newStatus >= MODULE_STATUS_ERRORED && newStatus <= MODULE_STATUS_EVALUATED,
+    assert(newStatus >= MODULE_STATUS_UNINSTANTIATED &&
+           newStatus <= MODULE_STATUS_EVALUATED_ERROR,
            "Bad new module status in ModuleSetStatus");
-    if (newStatus !== MODULE_STATUS_ERRORED)
-        assert(newStatus > module.status, "New module status inconsistent with current status");
+
+    // Note that under OOM conditions we can fail the module instantiation
+    // process even after modules have been marked as instantiated.
+    assert((module.status <= MODULE_STATUS_INSTANTIATED &&
+            newStatus === MODULE_STATUS_UNINSTANTIATED) ||
+           newStatus > module.status,
+           "New module status inconsistent with current status");
 
     UnsafeSetReservedSlot(module, MODULE_OBJECT_STATUS_SLOT, newStatus);
 }
@@ -80,20 +86,15 @@ function ModuleSetStatus(module, newStatus)
 // Returns an object describing the location of the resolved export or
 // indicating a failure.
 //
-// On success this returns: { resolved: true, module, bindingName }
+// On success this returns a resolved binding record: { module, bindingName }
 //
-// There are three failure cases:
+// There are two failure cases:
 //
-//  - The resolution failure can be blamed on a particular module.
-//    Returns: { resolved: false, module, ambiguous: false }
+//  - If no definition was found or the request is found to be circular, *null*
+//    is returned.
 //
-//  - No culprit can be determined and the resolution failure was due to star
-//    export ambiguity.
-//    Returns: { resolved: false, module: null, ambiguous: true }
-//
-//  - No culprit can be determined and the resolution failure was not due to
-//    star export ambiguity.
-//    Returns: { resolved: false, module: null, ambiguous: false }
+//  - If the request is found to be ambiguous, the string `"ambiguous"` is
+//    returned.
 //
 function ModuleResolveExport(exportName, resolveSet = [])
 {
@@ -106,53 +107,47 @@ function ModuleResolveExport(exportName, resolveSet = [])
     let module = this;
 
     // Step 2
-    assert(module.status !== MODULE_STATUS_ERRORED, "Bad module status in ResolveExport");
-    
-    // Step 3
     for (let i = 0; i < resolveSet.length; i++) {
         let r = resolveSet[i];
         if (r.module === module && r.exportName === exportName) {
             // This is a circular import request.
-            return {resolved: false, module: null, ambiguous: false};
+            return null;
         }
     }
 
-    // Step 4
+    // Step 3
     _DefineDataProperty(resolveSet, resolveSet.length, {module: module, exportName: exportName});
 
-    // Step 5
+    // Step 4
     let localExportEntries = module.localExportEntries;
     for (let i = 0; i < localExportEntries.length; i++) {
         let e = localExportEntries[i];
         if (exportName === e.exportName)
-            return {resolved: true, module, bindingName: e.localName};
+            return {module, bindingName: e.localName};
     }
 
-    // Step 6
+    // Step 5
     let indirectExportEntries = module.indirectExportEntries;
     for (let i = 0; i < indirectExportEntries.length; i++) {
         let e = indirectExportEntries[i];
         if (exportName === e.exportName) {
             let importedModule = CallModuleResolveHook(module, e.moduleRequest,
                                                        MODULE_STATUS_UNINSTANTIATED);
-            let resolution = callFunction(importedModule.resolveExport, importedModule, e.importName,
-                                          resolveSet);
-            if (!resolution.resolved && !resolution.module)
-                resolution.module = module;
-            return resolution;
+            return callFunction(importedModule.resolveExport, importedModule, e.importName,
+                                resolveSet);
         }
     }
 
-    // Step 7
+    // Step 6
     if (exportName === "default") {
         // A default export cannot be provided by an export *.
-        return {resolved: false, module: null, ambiguous: false};
+        return null;
     }
 
-    // Step 8
+    // Step 7
     let starResolution = null;
 
-    // Step 9
+    // Step 8
     let starExportEntries = module.starExportEntries;
     for (let i = 0; i < starExportEntries.length; i++) {
         let e = starExportEntries[i];
@@ -160,27 +155,31 @@ function ModuleResolveExport(exportName, resolveSet = [])
                                                    MODULE_STATUS_UNINSTANTIATED);
         let resolution = callFunction(importedModule.resolveExport, importedModule, exportName,
                                       resolveSet);
-        if (!resolution.resolved && (resolution.module || resolution.ambiguous))
+        if (resolution === "ambiguous")
             return resolution;
 
-        if (resolution.resolved) {
+        if (resolution !== null) {
             if (starResolution === null) {
                 starResolution = resolution;
             } else {
                 if (resolution.module !== starResolution.module ||
                     resolution.bindingName !== starResolution.bindingName)
                 {
-                    return {resolved: false, module: null, ambiguous: true};
+                    return "ambiguous";
                 }
             }
         }
     }
 
-    // Step 10
-    if (starResolution !== null)
-        return starResolution;
+    // Step 9
+    return starResolution;
+}
 
-    return {resolved: false, module: null, ambiguous: false};
+function IsResolvedBinding(resolution)
+{
+    assert(resolution === "ambiguous" || typeof resolution === "object",
+           "Bad module resolution result");
+    return typeof resolution === "object" && resolution !== null;
 }
 
 // 15.2.1.18 GetModuleNamespace(module)
@@ -189,12 +188,12 @@ function GetModuleNamespace(module)
     // Step 1
     assert(IsModule(module), "GetModuleNamespace called with non-module");
 
-    // Step 2
+    // Steps 2-3
     assert(module.status !== MODULE_STATUS_UNINSTANTIATED &&
-           module.status !== MODULE_STATUS_ERRORED,
+           module.status !== MODULE_STATUS_EVALUATED_ERROR,
            "Bad module status in GetModuleNamespace");
 
-    // Step 3
+    // Step 4
     let namespace = module.namespace;
 
     if (typeof namespace === "undefined") {
@@ -203,7 +202,7 @@ function GetModuleNamespace(module)
         for (let i = 0; i < exportedNames.length; i++) {
             let name = exportedNames[i];
             let resolution = callFunction(module.resolveExport, module, name);
-            if (resolution.resolved)
+            if (IsResolvedBinding(resolution))
                 _DefineDataProperty(unambiguousNames, unambiguousNames.length, name);
         }
         namespace = ModuleNamespaceCreate(module, unambiguousNames);
@@ -225,7 +224,7 @@ function ModuleNamespaceCreate(module, exports)
     for (let i = 0; i < exports.length; i++) {
         let name = exports[i];
         let binding = callFunction(module.resolveExport, module, name);
-        assert(binding.resolved, "Failed to resolve binding");
+        assert(IsResolvedBinding(binding), "Failed to resolve binding");
         AddModuleNamespaceBinding(ns, name, binding.module, binding.bindingName);
     }
 
@@ -236,31 +235,16 @@ function GetModuleEnvironment(module)
 {
     assert(IsModule(module), "Non-module passed to GetModuleEnvironment");
 
-    // Check for a previous failed attempt to instantiate this module. This can
-    // only happen due to a bug in the module loader.
-    if (module.status === MODULE_STATUS_ERRORED)
-        ThrowInternalError(JSMSG_MODULE_INSTANTIATE_FAILED, module.status);
+    assert(module.status >= MODULE_STATUS_INSTANTIATING,
+           "Attempt to access module environement before instantation");
 
     let env = UnsafeGetReservedSlot(module, MODULE_OBJECT_ENVIRONMENT_SLOT);
-    assert(env === undefined || IsModuleEnvironment(env),
+    assert(IsModuleEnvironment(env),
            "Module environment slot contains unexpected value");
 
     return env;
 }
 
-function RecordModuleError(module, error)
-{
-    // Set the module's status to 'errored' to indicate a failed module
-    // instantiation and record the exception. The environment slot is also
-    // reset to 'undefined'.
-
-    assert(IsObject(module) && IsModule(module), "Non-module passed to RecordModuleError");
-
-    ModuleSetStatus(module, MODULE_STATUS_ERRORED);
-    UnsafeSetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT, error);
-    UnsafeSetReservedSlot(module, MODULE_OBJECT_ENVIRONMENT_SLOT, undefined);
-}
-
 function CountArrayValues(array, value)
 {
     let count = 0;
@@ -280,6 +264,16 @@ function ArrayContains(array, value)
     return false;
 }
 
+function HandleModuleInstantiationFailure(module)
+{
+    // Reset the module to the "uninstantiated" state. Don't reset the
+    // environment slot as the environment object will be required by any
+    // possible future instantiation attempt.
+    ModuleSetStatus(module, MODULE_STATUS_UNINSTANTIATED);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_INDEX_SLOT, undefined);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT, undefined);
+}
+
 // 15.2.1.16.4 ModuleInstantiate()
 function ModuleInstantiate()
 {
@@ -301,38 +295,30 @@ function ModuleInstantiate()
 
     // Steps 4-5
     try {
-        InnerModuleDeclarationInstantiation(module, stack, 0);
+        InnerModuleInstantiation(module, stack, 0);
     } catch (error) {
         for (let i = 0; i < stack.length; i++) {
             let m = stack[i];
 
-            assert(m.status === MODULE_STATUS_INSTANTIATING ||
-                   m.status === MODULE_STATUS_ERRORED,
-                   "Bad module status after failed instantiation");
-
-            RecordModuleError(m, error);
+            assert(m.status === MODULE_STATUS_INSTANTIATING,
+                   "Expected instantiating status during failed instantiation");
+            HandleModuleInstantiationFailure(m);
         }
 
-        if (stack.length === 0 &&
-            typeof(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT)) === "undefined")
-        {
-            // This can happen due to OOM when appending to the stack.
-            assert(error === "out of memory",
-                   "Stack must contain module unless we hit OOM");
-            RecordModuleError(module, error);
-        }
+        // Handle OOM when appending to the stack or over-recursion errors.
+        if (stack.length === 0)
+            HandleModuleInstantiationFailure(module);
 
-        assert(module.status === MODULE_STATUS_ERRORED,
-               "Bad module status after failed instantiation");
-        assert(SameValue(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT), error),
-               "Module has different error set after failed instantiation");
+        assert(module.status === MODULE_STATUS_UNINSTANTIATED,
+               "Expected uninstantiated status after failed instantiation");
 
         throw error;
     }
 
     // Step 6
-    assert(module.status == MODULE_STATUS_INSTANTIATED ||
-           module.status == MODULE_STATUS_EVALUATED,
+    assert(module.status === MODULE_STATUS_INSTANTIATED ||
+           module.status === MODULE_STATUS_EVALUATED ||
+           module.status === MODULE_STATUS_EVALUATED_ERROR,
            "Bad module status after successful instantiation");
 
     // Step 7
@@ -344,8 +330,8 @@ function ModuleInstantiate()
 }
 _SetCanonicalName(ModuleInstantiate, "ModuleInstantiate");
 
-// 15.2.1.16.4.1 InnerModuleDeclarationInstantiation(module, stack, index)
-function InnerModuleDeclarationInstantiation(module, stack, index)
+// 15.2.1.16.4.1 InnerModuleInstantiation(module, stack, index)
+function InnerModuleInstantiation(module, stack, index)
 {
     // Step 1
     // TODO: Support module records other than source text module records.
@@ -353,42 +339,40 @@ function InnerModuleDeclarationInstantiation(module, stack, index)
     // Step 2
     if (module.status === MODULE_STATUS_INSTANTIATING ||
         module.status === MODULE_STATUS_INSTANTIATED ||
-        module.status === MODULE_STATUS_EVALUATED)
+        module.status === MODULE_STATUS_EVALUATED ||
+        module.status === MODULE_STATUS_EVALUATED_ERROR)
     {
         return index;
     }
 
     // Step 3
-    if (module.status === MODULE_STATUS_ERRORED)
-        throw module.error;
-
-    // Step 4
     assert(module.status === MODULE_STATUS_UNINSTANTIATED,
           "Bad module status in ModuleDeclarationInstantiation");
 
-    // Steps 5
+    // Step 4
     ModuleSetStatus(module, MODULE_STATUS_INSTANTIATING);
 
-    // Step 6-8
+    // Steps 5-7
     UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_INDEX_SLOT, index);
     UnsafeSetReservedSlot(module, MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT, index);
     index++;
 
-    // Step 9
+    // Step 8
     _DefineDataProperty(stack, stack.length, module);
 
-    // Step 10
+    // Step 9
     let requestedModules = module.requestedModules;
     for (let i = 0; i < requestedModules.length; i++) {
         let required = requestedModules[i];
-        let requiredModule = CallModuleResolveHook(module, required, MODULE_STATUS_ERRORED);
+        let requiredModule = CallModuleResolveHook(module, required, MODULE_STATUS_UNINSTANTIATED);
 
-        index = InnerModuleDeclarationInstantiation(requiredModule, stack, index);
+        index = InnerModuleInstantiation(requiredModule, stack, index);
 
         assert(requiredModule.status === MODULE_STATUS_INSTANTIATING ||
                requiredModule.status === MODULE_STATUS_INSTANTIATED ||
-               requiredModule.status === MODULE_STATUS_EVALUATED,
-               "Bad required module status after InnerModuleDeclarationInstantiation");
+               requiredModule.status === MODULE_STATUS_EVALUATED ||
+               requiredModule.status === MODULE_STATUS_EVALUATED_ERROR,
+               "Bad required module status after InnerModuleInstantiation");
 
         assert((requiredModule.status === MODULE_STATUS_INSTANTIATING) ===
                ArrayContains(stack, requiredModule),
@@ -404,16 +388,16 @@ function InnerModuleDeclarationInstantiation(module, stack, index)
         }
     }
 
-    // Step 11
+    // Step 10
     ModuleDeclarationEnvironmentSetup(module);
 
-    // Steps 12-13
+    // Steps 11-12
     assert(CountArrayValues(stack, module) === 1,
            "Current module should appear exactly once in the stack");
     assert(module.dfsAncestorIndex <= module.dfsIndex,
            "Bad DFS ancestor index");
 
-    // Step 14
+    // Step 13
     if (module.dfsAncestorIndex === module.dfsIndex) {
         let requiredModule;
         do {
@@ -434,16 +418,14 @@ function ModuleDeclarationEnvironmentSetup(module)
     for (let i = 0; i < indirectExportEntries.length; i++) {
         let e = indirectExportEntries[i];
         let resolution = callFunction(module.resolveExport, module, e.exportName);
-        assert(resolution.resolved || resolution.module,
-               "Unexpected failure to resolve export in ModuleDeclarationEnvironmentSetup");
-        if (!resolution.resolved) {
-            return ResolutionError(resolution, "indirectExport", e.exportName,
-                                   e.lineNumber, e.columnNumber)
+        if (!IsResolvedBinding(resolution)) {
+            ThrowResolutionError(module, resolution, "indirectExport", e.exportName,
+                                 e.lineNumber, e.columnNumber);
         }
     }
 
     // Steps 5-6
-    CreateModuleEnvironment(module);
+    // Note that we have already created the environment by this point.
     let env = GetModuleEnvironment(module);
 
     // Step 8
@@ -458,12 +440,9 @@ function ModuleDeclarationEnvironmentSetup(module)
         } else {
             let resolution = callFunction(importedModule.resolveExport, importedModule,
                                           imp.importName);
-            if (!resolution.resolved && !resolution.module)
-                resolution.module = module;
-
-            if (!resolution.resolved) {
-                return ResolutionError(resolution, "import", imp.importName,
-                                       imp.lineNumber, imp.columnNumber);
+            if (!IsResolvedBinding(resolution)) {
+                ThrowResolutionError(module, resolution, "import", imp.importName,
+                                     imp.lineNumber, imp.columnNumber);
             }
 
             CreateImportBinding(env, imp.localName, resolution.module, resolution.bindingName);
@@ -473,38 +452,58 @@ function ModuleDeclarationEnvironmentSetup(module)
     InstantiateModuleFunctionDeclarations(module);
 }
 
-// 15.2.1.16.4.3 ResolutionError(module)
-function ResolutionError(resolution, kind, name, line, column)
+function ThrowResolutionError(module, resolution, kind, name, line, column)
 {
-    let module = resolution.module;
-    assert(module !== null,
-           "Null module passed to ResolutionError");
-
-    assert(module.status === MODULE_STATUS_UNINSTANTIATED ||
-           module.status === MODULE_STATUS_INSTANTIATING,
-           "Unexpected module status in ResolutionError");
+    assert(module.status === MODULE_STATUS_INSTANTIATING,
+           "Unexpected module status in ThrowResolutionError");
 
     assert(kind === "import" || kind === "indirectExport",
-           "Unexpected kind in ResolutionError");
+           "Unexpected kind in ThrowResolutionError");
 
     assert(line > 0,
            "Line number should be present for all imports and indirect exports");
 
+    let ambiguous = resolution === "ambiguous";
+
     let errorNumber;
-    if (kind === "import") {
-        errorNumber = resolution.ambiguous ? JSMSG_AMBIGUOUS_IMPORT
-                                           : JSMSG_MISSING_IMPORT;
-    } else {
-        errorNumber = resolution.ambiguous ? JSMSG_AMBIGUOUS_INDIRECT_EXPORT
-                                           : JSMSG_MISSING_INDIRECT_EXPORT;
-    }
+    if (kind === "import")
+        errorNumber = ambiguous ? JSMSG_AMBIGUOUS_IMPORT : JSMSG_MISSING_IMPORT;
+    else
+        errorNumber = ambiguous ? JSMSG_AMBIGUOUS_INDIRECT_EXPORT : JSMSG_MISSING_INDIRECT_EXPORT;
 
     let message = GetErrorMessage(errorNumber) + ": " + name;
     let error = CreateModuleSyntaxError(module, line, column, message);
-    RecordModuleError(module, error);
     throw error;
 }
 
+function GetModuleEvaluationError(module)
+{
+    assert(IsObject(module) && IsModule(module),
+           "Non-module passed to GetModuleEvaluationError");
+    assert(module.status === MODULE_STATUS_EVALUATED_ERROR,
+           "Bad module status in GetModuleEvaluationError");
+    return UnsafeGetReservedSlot(module, MODULE_OBJECT_EVALUATION_ERROR_SLOT);
+}
+
+function RecordModuleEvaluationError(module, error)
+{
+    // Set the module's EvaluationError slot to indicate a failed module
+    // evaluation.
+
+    assert(IsObject(module) && IsModule(module),
+           "Non-module passed to RecordModuleEvaluationError");
+
+    if (module.status === MODULE_STATUS_EVALUATED_ERROR) {
+        // It would be nice to assert that |error| is the same as the one we
+        // previously recorded, but that's not always true in the case of out of
+        // memory and over-recursion errors.
+        return;
+    }
+
+    ModuleSetStatus(module, MODULE_STATUS_EVALUATED_ERROR);
+    UnsafeSetReservedSlot(module, MODULE_OBJECT_EVALUATION_ERROR_SLOT, error);
+}
+
 // 15.2.1.16.5 ModuleEvaluate()
 function ModuleEvaluate()
 {
@@ -515,9 +514,9 @@ function ModuleEvaluate()
     let module = this;
 
     // Step 2
-    if (module.status !== MODULE_STATUS_ERRORED &&
-        module.status !== MODULE_STATUS_INSTANTIATED &&
-        module.status !== MODULE_STATUS_EVALUATED)
+    if (module.status !== MODULE_STATUS_INSTANTIATED &&
+        module.status !== MODULE_STATUS_EVALUATED &&
+        module.status !== MODULE_STATUS_EVALUATED_ERROR)
     {
         ThrowInternalError(JSMSG_BAD_MODULE_STATUS);
     }
@@ -535,27 +534,20 @@ function ModuleEvaluate()
             assert(m.status === MODULE_STATUS_EVALUATING,
                    "Bad module status after failed evaluation");
 
-            RecordModuleError(m, error);
+            RecordModuleEvaluationError(m, error);
         }
 
-        if (stack.length === 0 &&
-            typeof(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT)) === "undefined")
-        {
-            // This can happen due to OOM when appending to the stack.
-            assert(error === "out of memory",
-                  "Stack must contain module unless we hit OOM");
-            RecordModuleError(module, error);
-        }
+        // Handle OOM when appending to the stack or over-recursion errors.
+        if (stack.length === 0)
+            RecordModuleEvaluationError(module, error);
 
-        assert(module.status === MODULE_STATUS_ERRORED,
+        assert(module.status === MODULE_STATUS_EVALUATED_ERROR,
                "Bad module status after failed evaluation");
-        assert(SameValue(UnsafeGetReservedSlot(module, MODULE_OBJECT_ERROR_SLOT), error),
-               "Module has different error set after failed evaluation");
 
         throw error;
     }
 
-    assert(module.status == MODULE_STATUS_EVALUATED,
+    assert(module.status === MODULE_STATUS_EVALUATED,
            "Bad module status after successful evaluation");
     assert(stack.length === 0,
            "Stack should be empty after successful evaluation");
@@ -571,19 +563,19 @@ function InnerModuleEvaluation(module, stack, index)
     // TODO: Support module records other than source text module records.
 
     // Step 2
-    if (module.status === MODULE_STATUS_EVALUATING ||
-        module.status === MODULE_STATUS_EVALUATED)
-    {
+    if (module.status === MODULE_STATUS_EVALUATED_ERROR)
+        throw GetModuleEvaluationError(module);
+
+    if (module.status === MODULE_STATUS_EVALUATED)
         return index;
-    }
 
     // Step 3
-    if (module.status === MODULE_STATUS_ERRORED)
-        throw module.error;
+    if (module.status === MODULE_STATUS_EVALUATING)
+        return index;
 
     // Step 4
     assert(module.status === MODULE_STATUS_INSTANTIATED,
-          "Bad module status in ModuleEvaluation");
+          "Bad module status in InnerModuleEvaluation");
 
     // Step 5
     ModuleSetStatus(module, MODULE_STATUS_EVALUATING);
@@ -605,8 +597,8 @@ function InnerModuleEvaluation(module, stack, index)
 
         index = InnerModuleEvaluation(requiredModule, stack, index);
 
-        assert(requiredModule.status == MODULE_STATUS_EVALUATING ||
-               requiredModule.status == MODULE_STATUS_EVALUATED,
+        assert(requiredModule.status === MODULE_STATUS_EVALUATING ||
+               requiredModule.status === MODULE_STATUS_EVALUATED,
               "Bad module status after InnerModuleEvaluation");
 
         assert((requiredModule.status === MODULE_STATUS_EVALUATING) ===
diff --git a/js/src/builtin/ModuleObject.cpp b/js/src/builtin/ModuleObject.cpp
index 30e7120c0..728929e8c 100644
--- a/js/src/builtin/ModuleObject.cpp
+++ b/js/src/builtin/ModuleObject.cpp
@@ -18,10 +18,10 @@
 using namespace js;
 using namespace js::frontend;
 
-static_assert(MODULE_STATUS_ERRORED < MODULE_STATUS_UNINSTANTIATED &&
-              MODULE_STATUS_UNINSTANTIATED < MODULE_STATUS_INSTANTIATING &&
+static_assert(MODULE_STATUS_UNINSTANTIATED < MODULE_STATUS_INSTANTIATING &&
               MODULE_STATUS_INSTANTIATING < MODULE_STATUS_INSTANTIATED &&
-              MODULE_STATUS_INSTANTIATED < MODULE_STATUS_EVALUATED,
+              MODULE_STATUS_INSTANTIATED < MODULE_STATUS_EVALUATED &&
+              MODULE_STATUS_EVALUATED < MODULE_STATUS_EVALUATED_ERROR,
               "Module statuses are ordered incorrectly");
 
 template<typename T, Value ValueGetter(const T* obj)>
@@ -248,21 +248,13 @@ IndirectBindingMap::Binding::Binding(ModuleEnvironmentObject* environment, Shape
   : environment(environment), shape(shape)
 {}
 
-IndirectBindingMap::IndirectBindingMap(Zone* zone)
-  : map_(ZoneAllocPolicy(zone))
-{
-}
-
-bool
-IndirectBindingMap::init()
-{
-    return map_.init();
-}
-
 void
 IndirectBindingMap::trace(JSTracer* trc)
 {
-    for (Map::Enum e(map_); !e.empty(); e.popFront()) {
+    if (!map_)
+        return;
+
+    for (Map::Enum e(*map_); !e.empty(); e.popFront()) {
         Binding& b = e.front().value();
         TraceEdge(trc, &b.environment, "module bindings environment");
         TraceEdge(trc, &b.shape, "module bindings shape");
@@ -273,12 +265,25 @@ IndirectBindingMap::trace(JSTracer* trc)
 }
 
 bool
-IndirectBindingMap::putNew(JSContext* cx, HandleId name,
-                           HandleModuleEnvironmentObject environment, HandleId localName)
+IndirectBindingMap::put(JSContext* cx, HandleId name,
+                        HandleModuleEnvironmentObject environment, HandleId localName)
 {
+    // This object might have been allocated on the background parsing thread in
+    // different zone to the final module. Lazily allocate the map so we don't
+    // have to switch its zone when merging compartments.
+    if (!map_) {
+        MOZ_ASSERT(!cx->zone()->usedByExclusiveThread);
+        map_.emplace(cx->zone());
+        if (!map_->init()) {
+            map_.reset();
+            ReportOutOfMemory(cx);
+            return false;
+        }
+    }
+
     RootedShape shape(cx, environment->lookup(cx, localName));
     MOZ_ASSERT(shape);
-    if (!map_.putNew(name, Binding(environment, shape))) {
+    if (!map_->put(name, Binding(environment, shape))) {
         ReportOutOfMemory(cx);
         return false;
     }
@@ -289,7 +294,10 @@ IndirectBindingMap::putNew(JSContext* cx, HandleId name,
 bool
 IndirectBindingMap::lookup(jsid name, ModuleEnvironmentObject** envOut, Shape** shapeOut) const
 {
-    auto ptr = map_.lookup(name);
+    if (!map_)
+        return false;
+
+    auto ptr = map_->lookup(name);
     if (!ptr)
         return false;
 
@@ -359,7 +367,7 @@ ModuleNamespaceObject::addBinding(JSContext* cx, HandleAtom exportedName,
     RootedModuleEnvironmentObject environment(cx, &targetModule->initialEnvironment());
     RootedId exportedNameId(cx, AtomToId(exportedName));
     RootedId localNameId(cx, AtomToId(localName));
-    return bindings->putNew(cx, exportedNameId, environment, localNameId);
+    return bindings->put(cx, exportedNameId, environment, localNameId);
 }
 
 const char ModuleNamespaceObject::ProxyHandler::family = 0;
@@ -625,10 +633,9 @@ ModuleObject::create(ExclusiveContext* cx)
     RootedModuleObject self(cx, &obj->as<ModuleObject>());
 
     Zone* zone = cx->zone();
-    IndirectBindingMap* bindings = zone->new_<IndirectBindingMap>(zone);
-    if (!bindings || !bindings->init()) {
+    IndirectBindingMap* bindings = zone->new_<IndirectBindingMap>();
+    if (!bindings) {
         ReportOutOfMemory(cx);
-        js_delete<IndirectBindingMap>(bindings);
         return nullptr;
     }
 
@@ -657,14 +664,24 @@ ModuleObject::finalize(js::FreeOp* fop, JSObject* obj)
         fop->delete_(funDecls);
 }
 
+ModuleEnvironmentObject&
+ModuleObject::initialEnvironment() const
+{
+    Value value = getReservedSlot(EnvironmentSlot);
+    return value.toObject().as<ModuleEnvironmentObject>();
+}
+
 ModuleEnvironmentObject*
 ModuleObject::environment() const
 {
-    Value value = getReservedSlot(EnvironmentSlot);
-    if (value.isUndefined())
+    MOZ_ASSERT(!hadEvaluationError());
+
+    // According to the spec the environment record is created during
+    // instantiation, but we create it earlier than that.
+    if (status() < MODULE_STATUS_INSTANTIATED)
         return nullptr;
 
-    return &value.toObject().as<ModuleEnvironmentObject>();
+    return &initialEnvironment();
 }
 
 bool
@@ -723,13 +740,13 @@ void
 ModuleObject::init(HandleScript script)
 {
     initReservedSlot(ScriptSlot, PrivateValue(script));
-    initReservedSlot(StatusSlot, Int32Value(MODULE_STATUS_ERRORED));
+    initReservedSlot(StatusSlot, Int32Value(MODULE_STATUS_UNINSTANTIATED));
 }
 
 void
 ModuleObject::setInitialEnvironment(HandleModuleEnvironmentObject initialEnvironment)
 {
-    initReservedSlot(InitialEnvironmentSlot, ObjectValue(*initialEnvironment));
+    initReservedSlot(EnvironmentSlot, ObjectValue(*initialEnvironment));
 }
 
 void
@@ -827,7 +844,8 @@ ModuleObject::script() const
 static inline void
 AssertValidModuleStatus(ModuleStatus status)
 {
-    MOZ_ASSERT(status >= MODULE_STATUS_ERRORED && status <= MODULE_STATUS_EVALUATED);
+    MOZ_ASSERT(status >= MODULE_STATUS_UNINSTANTIATED &&
+               status <= MODULE_STATUS_EVALUATED_ERROR);
 }
 
 ModuleStatus
@@ -838,11 +856,17 @@ ModuleObject::status() const
     return status;
 }
 
-Value
-ModuleObject::error() const
+bool
+ModuleObject::hadEvaluationError() const
 {
-    MOZ_ASSERT(status() == MODULE_STATUS_ERRORED);
-    return getReservedSlot(ErrorSlot);
+    return status() == MODULE_STATUS_EVALUATED_ERROR;
+}
+
+Value
+ModuleObject::evaluationError() const
+{
+    MOZ_ASSERT(hadEvaluationError());
+    return getReservedSlot(EvaluationErrorSlot);
 }
 
 Value
@@ -857,12 +881,6 @@ ModuleObject::setHostDefinedField(const JS::Value& value)
     setReservedSlot(HostDefinedSlot, value);
 }
 
-ModuleEnvironmentObject&
-ModuleObject::initialEnvironment() const
-{
-    return getReservedSlot(InitialEnvironmentSlot).toObject().as<ModuleEnvironmentObject>();
-}
-
 Scope*
 ModuleObject::enclosingScope() const
 {
@@ -888,16 +906,6 @@ ModuleObject::trace(JSTracer* trc, JSObject* obj)
         funDecls->trace(trc);
 }
 
-void
-ModuleObject::createEnvironment()
-{
-    // The environment has already been created, we just neet to set it in the
-    // right slot.
-    MOZ_ASSERT(!getReservedSlot(InitialEnvironmentSlot).isUndefined());
-    MOZ_ASSERT(getReservedSlot(EnvironmentSlot).isUndefined());
-    setReservedSlot(EnvironmentSlot, getReservedSlot(InitialEnvironmentSlot));
-}
-
 bool
 ModuleObject::noteFunctionDeclaration(ExclusiveContext* cx, HandleAtom name, HandleFunction fun)
 {
@@ -913,7 +921,10 @@ ModuleObject::noteFunctionDeclaration(ExclusiveContext* cx, HandleAtom name, Han
 /* static */ bool
 ModuleObject::instantiateFunctionDeclarations(JSContext* cx, HandleModuleObject self)
 {
+#ifdef DEBUG
+    MOZ_ASSERT(self->status() == MODULE_STATUS_INSTANTIATING);
     MOZ_ASSERT(IsFrozen(cx, self));
+#endif
 
     FunctionDeclarationVector* funDecls = self->functionDeclarations();
     if (!funDecls) {
@@ -944,7 +955,10 @@ ModuleObject::instantiateFunctionDeclarations(JSContext* cx, HandleModuleObject
 /* static */ bool
 ModuleObject::execute(JSContext* cx, HandleModuleObject self, MutableHandleValue rval)
 {
+#ifdef DEBUG
+    MOZ_ASSERT(self->status() == MODULE_STATUS_EVALUATING);
     MOZ_ASSERT(IsFrozen(cx, self));
+#endif
 
     RootedScript script(cx, self->script());
     RootedModuleEnvironmentObject scope(cx, self->environment());
@@ -967,10 +981,9 @@ ModuleObject::createNamespace(JSContext* cx, HandleModuleObject self, HandleObje
         return nullptr;
 
     Zone* zone = cx->zone();
-    IndirectBindingMap* bindings = zone->new_<IndirectBindingMap>(zone);
-    if (!bindings || !bindings->init()) {
+    IndirectBindingMap* bindings = zone->new_<IndirectBindingMap>();
+    if (!bindings) {
         ReportOutOfMemory(cx);
-        js_delete<IndirectBindingMap>(bindings);
         return nullptr;
     }
 
@@ -1005,7 +1018,7 @@ ModuleObject::Evaluate(JSContext* cx, HandleModuleObject self)
 
 DEFINE_GETTER_FUNCTIONS(ModuleObject, namespace_, NamespaceSlot)
 DEFINE_GETTER_FUNCTIONS(ModuleObject, status, StatusSlot)
-DEFINE_GETTER_FUNCTIONS(ModuleObject, error, ErrorSlot)
+DEFINE_GETTER_FUNCTIONS(ModuleObject, evaluationError, EvaluationErrorSlot)
 DEFINE_GETTER_FUNCTIONS(ModuleObject, requestedModules, RequestedModulesSlot)
 DEFINE_GETTER_FUNCTIONS(ModuleObject, importEntries, ImportEntriesSlot)
 DEFINE_GETTER_FUNCTIONS(ModuleObject, localExportEntries, LocalExportEntriesSlot)
@@ -1020,7 +1033,7 @@ GlobalObject::initModuleProto(JSContext* cx, Handle<GlobalObject*> global)
     static const JSPropertySpec protoAccessors[] = {
         JS_PSG("namespace", ModuleObject_namespace_Getter, 0),
         JS_PSG("status", ModuleObject_statusGetter, 0),
-        JS_PSG("error", ModuleObject_errorGetter, 0),
+        JS_PSG("evaluationError", ModuleObject_evaluationErrorGetter, 0),
         JS_PSG("requestedModules", ModuleObject_requestedModulesGetter, 0),
         JS_PSG("importEntries", ModuleObject_importEntriesGetter, 0),
         JS_PSG("localExportEntries", ModuleObject_localExportEntriesGetter, 0),
diff --git a/js/src/builtin/ModuleObject.h b/js/src/builtin/ModuleObject.h
index be0315215..5e4e7f342 100644
--- a/js/src/builtin/ModuleObject.h
+++ b/js/src/builtin/ModuleObject.h
@@ -7,6 +7,8 @@
 #ifndef builtin_ModuleObject_h
 #define builtin_ModuleObject_h
 
+#include "mozilla/Maybe.h"
+
 #include "jsapi.h"
 #include "jsatom.h"
 
@@ -102,27 +104,27 @@ typedef Handle<ExportEntryObject*> HandleExportEntryObject;
 class IndirectBindingMap
 {
   public:
-    explicit IndirectBindingMap(Zone* zone);
-    bool init();
-
     void trace(JSTracer* trc);
 
-    bool putNew(JSContext* cx, HandleId name,
-                HandleModuleEnvironmentObject environment, HandleId localName);
+    bool put(JSContext* cx, HandleId name,
+             HandleModuleEnvironmentObject environment, HandleId localName);
 
     size_t count() const {
-        return map_.count();
+        return map_ ? map_->count() : 0;
     }
 
     bool has(jsid name) const {
-        return map_.has(name);
+        return map_ ? map_->has(name) : false;
     }
 
     bool lookup(jsid name, ModuleEnvironmentObject** envOut, Shape** shapeOut) const;
 
     template <typename Func>
     void forEachExportedName(Func func) const {
-        for (auto r = map_.all(); !r.empty(); r.popFront())
+        if (!map_)
+            return;
+
+        for (auto r = map_->all(); !r.empty(); r.popFront())
             func(r.front().key());
     }
 
@@ -136,7 +138,7 @@ class IndirectBindingMap
 
     typedef HashMap<jsid, Binding, DefaultHasher<jsid>, ZoneAllocPolicy> Map;
 
-    Map map_;
+    mozilla::Maybe<Map> map_;
 };
 
 class ModuleNamespaceObject : public ProxyObject
@@ -214,11 +216,10 @@ class ModuleObject : public NativeObject
     enum
     {
         ScriptSlot = 0,
-        InitialEnvironmentSlot,
         EnvironmentSlot,
         NamespaceSlot,
         StatusSlot,
-        ErrorSlot,
+        EvaluationErrorSlot,
         HostDefinedSlot,
         RequestedModulesSlot,
         ImportEntriesSlot,
@@ -238,8 +239,8 @@ class ModuleObject : public NativeObject
                   "EnvironmentSlot must match self-hosting define");
     static_assert(StatusSlot == MODULE_OBJECT_STATUS_SLOT,
                   "StatusSlot must match self-hosting define");
-    static_assert(ErrorSlot == MODULE_OBJECT_ERROR_SLOT,
-                  "ErrorSlot must match self-hosting define");
+    static_assert(EvaluationErrorSlot == MODULE_OBJECT_EVALUATION_ERROR_SLOT,
+                  "EvaluationErrorSlot must match self-hosting define");
     static_assert(DFSIndexSlot == MODULE_OBJECT_DFS_INDEX_SLOT,
                   "DFSIndexSlot must match self-hosting define");
     static_assert(DFSAncestorIndexSlot == MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT,
@@ -269,7 +270,8 @@ class ModuleObject : public NativeObject
     ModuleEnvironmentObject* environment() const;
     ModuleNamespaceObject* namespace_();
     ModuleStatus status() const;
-    Value error() const;
+    bool hadEvaluationError() const;
+    Value evaluationError() const;
     Value hostDefinedField() const;
     ArrayObject& requestedModules() const;
     ArrayObject& importEntries() const;
@@ -285,9 +287,6 @@ class ModuleObject : public NativeObject
 
     void setHostDefinedField(const JS::Value& value);
 
-    // For intrinsic_CreateModuleEnvironment.
-    void createEnvironment();
-
     // For BytecodeEmitter.
     bool noteFunctionDeclaration(ExclusiveContext* cx, HandleAtom name, HandleFunction fun);
 
diff --git a/js/src/builtin/SelfHostingDefines.h b/js/src/builtin/SelfHostingDefines.h
index a06c2aa62..a3ba36804 100644
--- a/js/src/builtin/SelfHostingDefines.h
+++ b/js/src/builtin/SelfHostingDefines.h
@@ -97,17 +97,17 @@
 #define REGEXP_STRING_ITERATOR_FLAGS_SLOT 2
 #define REGEXP_STRING_ITERATOR_DONE_SLOT 3
 
-#define MODULE_OBJECT_ENVIRONMENT_SLOT        2
-#define MODULE_OBJECT_STATUS_SLOT             4
-#define MODULE_OBJECT_ERROR_SLOT              5
-#define MODULE_OBJECT_DFS_INDEX_SLOT          16
-#define MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT 17
+#define MODULE_OBJECT_ENVIRONMENT_SLOT        1
+#define MODULE_OBJECT_STATUS_SLOT             3
+#define MODULE_OBJECT_EVALUATION_ERROR_SLOT   4
+#define MODULE_OBJECT_DFS_INDEX_SLOT          15
+#define MODULE_OBJECT_DFS_ANCESTOR_INDEX_SLOT 16
 
-#define MODULE_STATUS_ERRORED        0
-#define MODULE_STATUS_UNINSTANTIATED 1
-#define MODULE_STATUS_INSTANTIATING  2
-#define MODULE_STATUS_INSTANTIATED   3
-#define MODULE_STATUS_EVALUATING     4
-#define MODULE_STATUS_EVALUATED      5
+#define MODULE_STATUS_UNINSTANTIATED  0
+#define MODULE_STATUS_INSTANTIATING   1
+#define MODULE_STATUS_INSTANTIATED    2
+#define MODULE_STATUS_EVALUATING      3
+#define MODULE_STATUS_EVALUATED       4
+#define MODULE_STATUS_EVALUATED_ERROR 5
 
 #endif
diff --git a/js/src/builtin/TestingFunctions.cpp b/js/src/builtin/TestingFunctions.cpp
index 025620766..f589b8076 100644
--- a/js/src/builtin/TestingFunctions.cpp
+++ b/js/src/builtin/TestingFunctions.cpp
@@ -3566,8 +3566,6 @@ GetModuleEnvironment(JSContext* cx, HandleValue moduleValue)
     // before they have been instantiated.
     RootedModuleEnvironmentObject env(cx, &module->initialEnvironment());
     MOZ_ASSERT(env);
-    MOZ_ASSERT_IF(module->environment(), module->environment() == env);
-
     return env;
 }
 
@@ -3585,6 +3583,9 @@ GetModuleEnvironmentNames(JSContext* cx, unsigned argc, Value* vp)
         return false;
     }
 
+//-    if (module->status() == MODULE_STATUS_ERRORED) {
+//+    if (module->hadEvaluationError()) {
+
     RootedModuleEnvironmentObject env(cx, GetModuleEnvironment(cx, args[0]));
     Rooted<IdVector> ids(cx, IdVector(cx));
     if (!JS_Enumerate(cx, env, &ids))
@@ -3622,6 +3623,9 @@ GetModuleEnvironmentValue(JSContext* cx, unsigned argc, Value* vp)
         return false;
     }
 
+//-    if (module->status() == MODULE_STATUS_ERRORED) {
+//+    if (module->hadEvaluationError()) {
+
     RootedModuleEnvironmentObject env(cx, GetModuleEnvironment(cx, args[0]));
     RootedString name(cx, args[1].toString());
     RootedId id(cx);
diff --git a/js/src/jit-test/tests/modules/bug-1284486.js b/js/src/jit-test/tests/modules/bug-1284486.js
index 08286393a..6fbd67d9d 100644
--- a/js/src/jit-test/tests/modules/bug-1284486.js
+++ b/js/src/jit-test/tests/modules/bug-1284486.js
@@ -1,9 +1,8 @@
-// This tests that attempting to perform ModuleDeclarationInstantation a second
-// time after a failure re-throws the same error.
+// This tests that module instantiation can succeed when executed a second
+// time after a failure.
 //
 // The first attempt fails becuase module 'a' is not available. The second
-// attempt fails because of the previous failure (it would otherwise succeed as
-// 'a' is now available).
+// attempt succeeds as 'a' is now available.
 
 load(libdir + "dummyModuleResolveHook.js");
 
@@ -25,12 +24,9 @@ let a = moduleRepo['a'] = parseModule("export var a = 1; export var b = 2;");
 let d = moduleRepo['d'] = parseModule("import { a } from 'c'; a;");
 
 threw = false;
-let e2;
 try {
     d.declarationInstantiation();
 } catch (exc) {
     threw = true;
-    e2 = exc;
 }
-assertEq(threw, true);
-assertEq(e1, e2);
+assertEq(threw, false);
diff --git a/js/src/jit-test/tests/modules/bug-1420420-2.js b/js/src/jit-test/tests/modules/bug-1420420-2.js
new file mode 100644
index 000000000..0511e8126
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1420420-2.js
@@ -0,0 +1,19 @@
+// Test re-instantiation module after failure.
+
+load(libdir + "asserts.js");
+load(libdir + "dummyModuleResolveHook.js");
+
+moduleRepo["good"] = parseModule(`export let x`);
+
+moduleRepo["y1"] = parseModule(`export let y`);
+moduleRepo["y2"] = parseModule(`export let y`);
+moduleRepo["bad"] = parseModule(`export* from "y1"; export* from "y2";`);
+
+moduleRepo["a"] = parseModule(`import* as ns from "good"; import {y} from "bad";`);
+
+let b = moduleRepo["b"] = parseModule(`import "a";`);
+let c = moduleRepo["c"] = parseModule(`import "a";`);
+
+assertThrowsInstanceOf(() => b.declarationInstantiation(), SyntaxError);
+assertThrowsInstanceOf(() => c.declarationInstantiation(), SyntaxError);
+
diff --git a/js/src/jit-test/tests/modules/bug-1420420-3.js b/js/src/jit-test/tests/modules/bug-1420420-3.js
new file mode 100644
index 000000000..236c023b9
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1420420-3.js
@@ -0,0 +1,9 @@
+if (!('stackTest' in this))
+   quit();
+
+let a = parseModule(`throw new Error`);
+a.declarationInstantiation();
+stackTest(function() {
+    a.evaluation();
+});
+
diff --git a/js/src/jit-test/tests/modules/bug-1420420-4.js b/js/src/jit-test/tests/modules/bug-1420420-4.js
new file mode 100644
index 000000000..721c770bc
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1420420-4.js
@@ -0,0 +1,16 @@
+load(libdir + "asserts.js");
+load(libdir + "dummyModuleResolveHook.js");
+
+moduleRepo["a"] = parseModule(`throw undefined`);
+
+let b = moduleRepo["b"] = parseModule(`import "a";`);
+let c = moduleRepo["c"] = parseModule(`import "a";`);
+
+b.declarationInstantiation();
+c.declarationInstantiation();
+
+let count = 0;
+try { b.evaluation() } catch (e) { count++; }
+try { c.evaluation() } catch (e) { count++; }
+assertEq(count, 2);
+
diff --git a/js/src/jit-test/tests/modules/bug-1420420.js b/js/src/jit-test/tests/modules/bug-1420420.js
new file mode 100644
index 000000000..cd1101c76
--- /dev/null
+++ b/js/src/jit-test/tests/modules/bug-1420420.js
@@ -0,0 +1,19 @@
+// Test re-instantiation module after failure.
+
+load(libdir + "asserts.js");
+load(libdir + "dummyModuleResolveHook.js");
+
+moduleRepo["good"] = parseModule(`export let x`);
+
+moduleRepo["y1"] = parseModule(`export let y`);
+moduleRepo["y2"] = parseModule(`export let y`);
+moduleRepo["bad"] = parseModule(`export* from "y1"; export* from "y2";`);
+
+moduleRepo["a"] = parseModule(`import {x} from "good"; import {y} from "bad";`);
+
+let b = moduleRepo["b"] = parseModule(`import "a";`);
+let c = moduleRepo["c"] = parseModule(`import "a";`);
+
+assertThrowsInstanceOf(() => b.declarationInstantiation(), SyntaxError);
+assertThrowsInstanceOf(() => c.declarationInstantiation(), SyntaxError);
+
diff --git a/js/src/js.msg b/js/src/js.msg
index 9c508ebbd..587481864 100644
--- a/js/src/js.msg
+++ b/js/src/js.msg
@@ -579,7 +579,6 @@ MSG_DEF(JSMSG_MISSING_IMPORT,            0, JSEXN_SYNTAXERR, "import not found")
 MSG_DEF(JSMSG_AMBIGUOUS_IMPORT,          0, JSEXN_SYNTAXERR, "ambiguous import")
 MSG_DEF(JSMSG_MISSING_NAMESPACE_EXPORT,  0, JSEXN_SYNTAXERR, "export not found for namespace")
 MSG_DEF(JSMSG_MISSING_EXPORT,            1, JSEXN_SYNTAXERR, "local binding for export '{0}' not found")
-MSG_DEF(JSMSG_MODULE_INSTANTIATE_FAILED, 0, JSEXN_INTERNALERR, "attempt to re-instantiate module after failure")
 MSG_DEF(JSMSG_BAD_MODULE_STATUS,         0, JSEXN_INTERNALERR, "module record has unexpected status")
 
 // Promise
diff --git a/js/src/jsapi.cpp b/js/src/jsapi.cpp
index cf5880e03..6f66f4c8f 100644
--- a/js/src/jsapi.cpp
+++ b/js/src/jsapi.cpp
@@ -4662,21 +4662,16 @@ JS::Evaluate(JSContext* cx, const ReadOnlyCompileOptions& optionsArg,
     return ::Evaluate(cx, optionsArg, filename, rval);
 }
 
-JS_PUBLIC_API(JSFunction*)
-JS::GetModuleResolveHook(JSContext* cx)
+JS_PUBLIC_API(JS::ModuleResolveHook)
+JS::GetModuleResolveHook(JSRuntime* rt)
 {
-    AssertHeapIsIdle(cx);
-    CHECK_REQUEST(cx);
-    return cx->global()->moduleResolveHook();
+    return rt->moduleResolveHook;
 }
 
 JS_PUBLIC_API(void)
-JS::SetModuleResolveHook(JSContext* cx, HandleFunction func)
+JS::SetModuleResolveHook(JSRuntime* rt, JS::ModuleResolveHook func)
 {
-    AssertHeapIsIdle(cx);
-    CHECK_REQUEST(cx);
-    assertSameCompartment(cx, func);
-    cx->global()->setModuleResolveHook(func);
+    rt->moduleResolveHook = func;
 }
 
 JS_PUBLIC_API(bool)
@@ -4739,18 +4734,6 @@ JS::GetModuleScript(JSContext* cx, JS::HandleObject moduleArg)
     return moduleArg->as<ModuleObject>().script();
 }
 
-JS_PUBLIC_API(bool)
-JS::IsModuleErrored(JSObject* moduleArg)
-{
-    return moduleArg->as<ModuleObject>().status() == MODULE_STATUS_ERRORED;
-}
-
-JS_PUBLIC_API(JS::Value)
-JS::GetModuleError(JSObject* moduleArg)
-{
-    return moduleArg->as<ModuleObject>().error();
-}
-
 JS_PUBLIC_API(JSObject*)
 JS_New(JSContext* cx, HandleObject ctor, const JS::HandleValueArray& inputArgs)
 {
diff --git a/js/src/jsapi.h b/js/src/jsapi.h
index 9c3bf8151..56c54dcd2 100644
--- a/js/src/jsapi.h
+++ b/js/src/jsapi.h
@@ -4322,17 +4322,19 @@ extern JS_PUBLIC_API(bool)
 Evaluate(JSContext* cx, const ReadOnlyCompileOptions& options,
          const char* filename, JS::MutableHandleValue rval);
 
-/**
- * Get the HostResolveImportedModule hook for a global.
- */
-extern JS_PUBLIC_API(JSFunction*)
-GetModuleResolveHook(JSContext* cx);
+using ModuleResolveHook = JSObject* (*)(JSContext*, HandleObject, HandleString);
 
 /**
- * Set the HostResolveImportedModule hook for a global to the given function.
+ * Get the HostResolveImportedModule hook for the runtime.
+ */
+extern JS_PUBLIC_API(ModuleResolveHook)
+GetModuleResolveHook(JSRuntime* rt);
+
+/**
+ * Set the HostResolveImportedModule hook for the runtime to the given function.
  */
 extern JS_PUBLIC_API(void)
-SetModuleResolveHook(JSContext* cx, JS::HandleFunction func);
+SetModuleResolveHook(JSRuntime* rt, ModuleResolveHook func);
 
 /**
  * Parse the given source buffer as a module in the scope of the current global
@@ -4395,12 +4397,6 @@ GetRequestedModules(JSContext* cx, JS::HandleObject moduleRecord);
 extern JS_PUBLIC_API(JSScript*)
 GetModuleScript(JSContext* cx, JS::HandleObject moduleRecord);
 
-extern JS_PUBLIC_API(bool)
-IsModuleErrored(JSObject* moduleRecord);
-
-extern JS_PUBLIC_API(JS::Value)
-GetModuleError(JSObject* moduleRecord);
-
 } /* namespace JS */
 
 extern JS_PUBLIC_API(bool)
diff --git a/js/src/shell/js.cpp b/js/src/shell/js.cpp
index 8cd821b31..bbf35459f 100644
--- a/js/src/shell/js.cpp
+++ b/js/src/shell/js.cpp
@@ -274,6 +274,7 @@ struct ShellContext
     JS::PersistentRooted<JobQueue> jobQueue;
     ExclusiveData<ShellAsyncTasks> asyncTasks;
     bool drainingJobQueue;
+    JS::PersistentRootedFunction moduleResolveHook;
 
     /*
      * Watchdog thread state.
@@ -439,7 +440,8 @@ ShellContext::ShellContext(JSContext* cx)
     exitCode(0),
     quitting(false),
     readLineBufPos(0),
-    spsProfilingStackSize(0)
+    spsProfilingStackSize(0),
+    moduleResolveHook(cx)
 {}
 
 static ShellContext*
@@ -4030,13 +4032,34 @@ SetModuleResolveHook(JSContext* cx, unsigned argc, Value* vp)
         return false;
     }
 
-    RootedFunction hook(cx, &args[0].toObject().as<JSFunction>());
-    Rooted<GlobalObject*> global(cx, cx->global());
-    global->setModuleResolveHook(hook);
+    ShellContext* sc = GetShellContext(cx);
+    sc->moduleResolveHook = &args[0].toObject().as<JSFunction>();
+
     args.rval().setUndefined();
     return true;
 }
 
+static JSObject*
+CallModuleResolveHook(JSContext* cx, HandleObject module, HandleString specifier)
+{
+    ShellContext* sc = GetShellContext(cx);
+
+    JS::AutoValueArray<2> args(cx);
+    args[0].setObject(*module);
+    args[1].setString(specifier);
+
+    RootedValue result(cx);
+    if (!JS_CallFunction(cx, nullptr, sc->moduleResolveHook, args, &result))
+        return nullptr;
+
+    if (!result.isObject() || !result.toObject().is<ModuleObject>()) {
+         JS_ReportErrorASCII(cx, "Module resolve hook did not return Module object");
+         return nullptr;
+    }
+
+    return &result.toObject();
+}
+
 static bool
 GetModuleLoadPath(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -7962,6 +7985,8 @@ main(int argc, char** argv, char** envp)
 
     js::SetPreserveWrapperCallback(cx, DummyPreserveWrapperCallback);
 
+    JS::SetModuleResolveHook(cx->runtime(), CallModuleResolveHook);
+
     result = Shell(cx, &op, envp);
 
 #ifdef DEBUG
diff --git a/js/src/vm/EnvironmentObject.cpp b/js/src/vm/EnvironmentObject.cpp
index 7834940f1..871ae3f19 100644
--- a/js/src/vm/EnvironmentObject.cpp
+++ b/js/src/vm/EnvironmentObject.cpp
@@ -491,7 +491,7 @@ ModuleEnvironmentObject::createImportBinding(JSContext* cx, HandleAtom importNam
     RootedId importNameId(cx, AtomToId(importName));
     RootedId localNameId(cx, AtomToId(localName));
     RootedModuleEnvironmentObject env(cx, &module->initialEnvironment());
-    if (!importBindings().putNew(cx, importNameId, env, localNameId)) {
+    if (!importBindings().put(cx, importNameId, env, localNameId)) {
         ReportOutOfMemory(cx);
         return false;
     }
diff --git a/js/src/vm/GlobalObject.h b/js/src/vm/GlobalObject.h
index 720f63e69..a9f07d495 100644
--- a/js/src/vm/GlobalObject.h
+++ b/js/src/vm/GlobalObject.h
@@ -119,7 +119,6 @@ class GlobalObject : public NativeObject
         DEBUGGERS,
         INTRINSICS,
         FOR_OF_PIC_CHAIN,
-        MODULE_RESOLVE_HOOK,
         WINDOW_PROXY,
         GLOBAL_THIS_RESOLVED,
 
@@ -879,19 +878,6 @@ class GlobalObject : public NativeObject
         setReservedSlot(WINDOW_PROXY, ObjectValue(*windowProxy));
     }
 
-    void setModuleResolveHook(HandleFunction hook) {
-        MOZ_ASSERT(hook);
-        setSlot(MODULE_RESOLVE_HOOK, ObjectValue(*hook));
-    }
-
-    JSFunction* moduleResolveHook() {
-        Value value = getSlotRef(MODULE_RESOLVE_HOOK);
-        if (value.isUndefined())
-            return nullptr;
-
-        return &value.toObject().as<JSFunction>();
-    }
-
     // Returns either this global's star-generator function prototype, or null
     // if that object was never created.  Dodgy; for use only in also-dodgy
     // GlobalHelperThreadState::mergeParseTaskCompartment().
diff --git a/js/src/vm/Runtime.cpp b/js/src/vm/Runtime.cpp
index 284a4f3d7..5e0246b85 100644
--- a/js/src/vm/Runtime.cpp
+++ b/js/src/vm/Runtime.cpp
@@ -241,8 +241,10 @@ JSRuntime::JSRuntime(JSRuntime* parentRuntime)
     lastAnimationTime(0),
     performanceMonitoring(thisFromCtor()),
     ionLazyLinkListSize_(0),
-    stackFormat_(parentRuntime ? js::StackFormat::Default
-                               : js::StackFormat::SpiderMonkey)
+    stackFormat_(parentRuntime ?
+                 js::StackFormat::Default :
+                 js::StackFormat::SpiderMonkey),
+    moduleResolveHook()
 {
     setGCStoreBufferPtr(&gc.storeBuffer);
 
diff --git a/js/src/vm/Runtime.h b/js/src/vm/Runtime.h
index e60371e38..247a2dc9d 100644
--- a/js/src/vm/Runtime.h
+++ b/js/src/vm/Runtime.h
@@ -1294,6 +1294,9 @@ struct JSRuntime : public JS::shadow::Runtime,
     // For inherited heap state accessors.
     friend class js::gc::AutoTraceSession;
     friend class JS::AutoEnterCycleCollection;
+
+    // The implementation-defined abstract operation HostResolveImportedModule.
+    JS::ModuleResolveHook moduleResolveHook;
 };
 
 namespace js {
diff --git a/js/src/vm/SelfHosting.cpp b/js/src/vm/SelfHosting.cpp
index 0dfeffc36..f324a0a67 100644
--- a/js/src/vm/SelfHosting.cpp
+++ b/js/src/vm/SelfHosting.cpp
@@ -2026,36 +2026,26 @@ intrinsic_HostResolveImportedModule(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
     MOZ_ASSERT(args.length() == 2);
-    MOZ_ASSERT(args[0].toObject().is<ModuleObject>());
-    MOZ_ASSERT(args[1].isString());
+    RootedModuleObject module(cx, &args[0].toObject().as<ModuleObject>());
+    RootedString specifier(cx, args[1].toString());
 
-    RootedFunction moduleResolveHook(cx, cx->global()->moduleResolveHook());
+    JS::ModuleResolveHook moduleResolveHook = cx->runtime()->moduleResolveHook;
     if (!moduleResolveHook) {
         JS_ReportErrorASCII(cx, "Module resolve hook not set");
         return false;
     }
 
-    RootedValue result(cx);
-    if (!JS_CallFunction(cx, nullptr, moduleResolveHook, args, &result))
+    RootedObject result(cx);
+    result = moduleResolveHook(cx, module, specifier);
+    if (!result)
         return false;
 
-    if (!result.isObject() || !result.toObject().is<ModuleObject>()) {
+    if (!result->is<ModuleObject>()) {
         JS_ReportErrorASCII(cx, "Module resolve hook did not return Module object");
         return false;
     }
 
-    args.rval().set(result);
-    return true;
-}
-
-static bool
-intrinsic_CreateModuleEnvironment(JSContext* cx, unsigned argc, Value* vp)
-{
-    CallArgs args = CallArgsFromVp(argc, vp);
-    MOZ_ASSERT(args.length() == 1);
-    RootedModuleObject module(cx, &args[0].toObject().as<ModuleObject>());
-    module->createEnvironment();
-    args.rval().setUndefined();
+    args.rval().setObject(*result);
     return true;
 }
 
@@ -2087,7 +2077,6 @@ intrinsic_CreateNamespaceBinding(JSContext* cx, unsigned argc, Value* vp)
     // the slot directly.
     RootedShape shape(cx, environment->lookup(cx, name));
     MOZ_ASSERT(shape);
-    MOZ_ASSERT(environment->getSlot(shape->slot()).isMagic(JS_UNINITIALIZED_LEXICAL));
     environment->setSlot(shape->slot(), args[2]);
     args.rval().setUndefined();
     return true;
@@ -2659,7 +2648,6 @@ static const JSFunctionSpec intrinsic_functions[] = {
           CallNonGenericSelfhostedMethod<Is<ModuleObject>>, 2, 0),
     JS_FN("HostResolveImportedModule", intrinsic_HostResolveImportedModule, 2, 0),
     JS_FN("IsModuleEnvironment", intrinsic_IsInstanceOfBuiltin<ModuleEnvironmentObject>, 1, 0),
-    JS_FN("CreateModuleEnvironment", intrinsic_CreateModuleEnvironment, 1, 0),
     JS_FN("CreateImportBinding", intrinsic_CreateImportBinding, 4, 0),
     JS_FN("CreateNamespaceBinding", intrinsic_CreateNamespaceBinding, 3, 0),
     JS_FN("InstantiateModuleFunctionDeclarations",
diff --git a/parser/html/nsHtml5SpeculativeLoad.cpp b/parser/html/nsHtml5SpeculativeLoad.cpp
index 8ffc4d063..7bae0699f 100644
--- a/parser/html/nsHtml5SpeculativeLoad.cpp
+++ b/parser/html/nsHtml5SpeculativeLoad.cpp
@@ -6,9 +6,12 @@
 #include "nsHtml5TreeOpExecutor.h"
 
 nsHtml5SpeculativeLoad::nsHtml5SpeculativeLoad()
+ :
 #ifdef DEBUG
- : mOpCode(eSpeculativeLoadUninitialized)
+  mOpCode(eSpeculativeLoadUninitialized),
 #endif
+  mIsAsync(false),
+  mIsDefer(false)
 {
   MOZ_COUNT_CTOR(nsHtml5SpeculativeLoad);
 }
@@ -48,11 +51,13 @@ nsHtml5SpeculativeLoad::Perform(nsHtml5TreeOpExecutor* aExecutor)
       break;
     case eSpeculativeLoadScript:
       aExecutor->PreloadScript(mUrl, mCharset, mTypeOrCharsetSourceOrDocumentMode,
-                               mCrossOrigin, mIntegrity, false);
+                               mCrossOrigin, mIntegrity, false,
+                               mIsAsync, mIsDefer);
       break;
     case eSpeculativeLoadScriptFromHead:
       aExecutor->PreloadScript(mUrl, mCharset, mTypeOrCharsetSourceOrDocumentMode,
-                               mCrossOrigin, mIntegrity, true);
+                               mCrossOrigin, mIntegrity, true,
+                               mIsAsync, mIsDefer);
       break;
     case eSpeculativeLoadStyle:
       aExecutor->PreloadStyle(mUrl, mCharset, mCrossOrigin, mIntegrity);
diff --git a/parser/html/nsHtml5SpeculativeLoad.h b/parser/html/nsHtml5SpeculativeLoad.h
index 6f1365bcf..fcc84de4f 100644
--- a/parser/html/nsHtml5SpeculativeLoad.h
+++ b/parser/html/nsHtml5SpeculativeLoad.h
@@ -128,7 +128,9 @@ class nsHtml5SpeculativeLoad {
                            nsHtml5String aType,
                            nsHtml5String aCrossOrigin,
                            nsHtml5String aIntegrity,
-                           bool aParserInHead)
+                           bool aParserInHead,
+                           bool aAsync,
+                           bool aDefer)
     {
       NS_PRECONDITION(mOpCode == eSpeculativeLoadUninitialized,
                       "Trying to reinitialize a speculative load!");
@@ -139,6 +141,8 @@ class nsHtml5SpeculativeLoad {
       aType.ToString(mTypeOrCharsetSourceOrDocumentMode);
       aCrossOrigin.ToString(mCrossOrigin);
       aIntegrity.ToString(mIntegrity);
+      mIsAsync = aAsync;
+      mIsDefer = aDefer;
     }
 
     inline void InitStyle(nsHtml5String aUrl,
@@ -221,6 +225,13 @@ class nsHtml5SpeculativeLoad {
 
   private:
     eHtml5SpeculativeLoad mOpCode;
+
+    /**
+     * Whether the refering element has async and/or defer attributes.
+     */
+    bool mIsAsync;
+    bool mIsDefer;
+
     nsString mUrl;
     nsString mReferrerPolicy;
     nsString mMetaCSP;
diff --git a/parser/html/nsHtml5TreeBuilderCppSupplement.h b/parser/html/nsHtml5TreeBuilderCppSupplement.h
index 62df6d002..2ad87f795 100644
--- a/parser/html/nsHtml5TreeBuilderCppSupplement.h
+++ b/parser/html/nsHtml5TreeBuilderCppSupplement.h
@@ -185,16 +185,20 @@ nsHtml5TreeBuilder::createElement(int32_t aNamespace,
               aAttributes->getValue(nsHtml5AttributeName::ATTR_CROSSORIGIN);
             nsHtml5String integrity =
               aAttributes->getValue(nsHtml5AttributeName::ATTR_INTEGRITY);
+            bool async =
+              aAttributes->contains(nsHtml5AttributeName::ATTR_ASYNC);
+            bool defer =
+              aAttributes->contains(nsHtml5AttributeName::ATTR_DEFER);
             mSpeculativeLoadQueue.AppendElement()->InitScript(
               url,
               charset,
               type,
               crossOrigin,
               integrity,
-              mode == nsHtml5TreeBuilder::IN_HEAD);
-            mCurrentHtmlScriptIsAsyncOrDefer =
-              aAttributes->contains(nsHtml5AttributeName::ATTR_ASYNC) ||
-              aAttributes->contains(nsHtml5AttributeName::ATTR_DEFER);
+              mode == nsHtml5TreeBuilder::IN_HEAD,
+              async,
+              defer);
+            mCurrentHtmlScriptIsAsyncOrDefer = async || defer;
           }
         } else if (nsHtml5Atoms::link == aName) {
           nsHtml5String rel =
@@ -297,7 +301,9 @@ nsHtml5TreeBuilder::createElement(int32_t aNamespace,
               type,
               crossOrigin,
               integrity,
-              mode == nsHtml5TreeBuilder::IN_HEAD);
+              mode == nsHtml5TreeBuilder::IN_HEAD,
+              false /* async */, 
+              false /* defer */);
           }
         } else if (nsHtml5Atoms::style == aName) {
           nsHtml5TreeOperation* treeOp = mOpQueue.AppendElement();
diff --git a/parser/html/nsHtml5TreeOpExecutor.cpp b/parser/html/nsHtml5TreeOpExecutor.cpp
index 3ed634d0c..9be7f3b0d 100644
--- a/parser/html/nsHtml5TreeOpExecutor.cpp
+++ b/parser/html/nsHtml5TreeOpExecutor.cpp
@@ -921,14 +921,16 @@ nsHtml5TreeOpExecutor::PreloadScript(const nsAString& aURL,
                                      const nsAString& aType,
                                      const nsAString& aCrossOrigin,
                                      const nsAString& aIntegrity,
-                                     bool aScriptFromHead)
+                                     bool aScriptFromHead,
+                                     bool aAsync,
+                                     bool aDefer)
 {
   nsCOMPtr<nsIURI> uri = ConvertIfNotPreloadedYet(aURL);
   if (!uri) {
     return;
   }
   mDocument->ScriptLoader()->PreloadURI(uri, aCharset, aType, aCrossOrigin,
-                                        aIntegrity, aScriptFromHead,
+                                        aIntegrity, aScriptFromHead, aAsync, aDefer,
                                         mSpeculationReferrerPolicy);
 }
 
diff --git a/parser/html/nsHtml5TreeOpExecutor.h b/parser/html/nsHtml5TreeOpExecutor.h
index c4b6a4594..64a5daa96 100644
--- a/parser/html/nsHtml5TreeOpExecutor.h
+++ b/parser/html/nsHtml5TreeOpExecutor.h
@@ -249,7 +249,9 @@ class nsHtml5TreeOpExecutor final : public nsHtml5DocumentBuilder,
                        const nsAString& aType,
                        const nsAString& aCrossOrigin,
                        const nsAString& aIntegrity,
-                       bool aScriptFromHead);
+                       bool aScriptFromHead,
+                       bool aAsync,
+                       bool aDefer);
 
     void PreloadStyle(const nsAString& aURL, const nsAString& aCharset,
                       const nsAString& aCrossOrigin,
diff --git a/parser/html/nsHtml5TreeOperation.cpp b/parser/html/nsHtml5TreeOperation.cpp
index 46907d3a4..6444b9674 100644
--- a/parser/html/nsHtml5TreeOperation.cpp
+++ b/parser/html/nsHtml5TreeOperation.cpp
@@ -1076,7 +1076,7 @@ nsHtml5TreeOperation::Perform(nsHtml5TreeOpExecutor* aBuilder,
       nsCOMPtr<nsIScriptElement> sele = do_QueryInterface(node);
       NS_ASSERTION(sele, "Node didn't QI to script.");
       sele->SetScriptLineNumber(mFour.integer);
-      sele->FreezeUriAsyncDefer();
+      sele->FreezeExecutionAttrs(node->OwnerDoc());
       return NS_OK;
     }
     case eTreeOpSvgLoad: {