diff --git a/dom/security/nsContentSecurityManager.cpp b/dom/security/nsContentSecurityManager.cpp
index 12c55e8f6..08fd9afd9 100644
--- a/dom/security/nsContentSecurityManager.cpp
+++ b/dom/security/nsContentSecurityManager.cpp
@@ -95,9 +95,11 @@ nsContentSecurityManager::AllowTopLevelNavigationToDataURI(nsIChannel* aChannel)
 /* static */ nsresult
 nsContentSecurityManager::CheckFTPSubresourceLoad(nsIChannel* aChannel)
 {
-  // We dissallow using FTP resources as a subresource everywhere.
+  // We dissallow using FTP resources as a subresource almost everywhere.
   // The only valid way to use FTP resources is loading it as
   // a top level document.
+  
+  // Override blocking if the pref is set to allow.
   if (!mozilla::net::nsIOService::BlockFTPSubresources()) {
     return NS_OK;
   }
@@ -108,6 +110,13 @@ nsContentSecurityManager::CheckFTPSubresourceLoad(nsIChannel* aChannel)
   }
 
   nsContentPolicyType type = loadInfo->GetExternalContentPolicyType();
+
+  // Allow save-as download of FTP files on HTTP pages.
+  if (type == nsIContentPolicy::TYPE_SAVEAS_DOWNLOAD) {
+    return NS_OK;
+  }
+
+  // Allow direct document requests
   if (type == nsIContentPolicy::TYPE_DOCUMENT) {
     return NS_OK;
   }
@@ -119,11 +128,22 @@ nsContentSecurityManager::CheckFTPSubresourceLoad(nsIChannel* aChannel)
     return NS_OK;
   }
 
+  // Allow if it's not the FTP protocol
   bool isFtpURI = (NS_SUCCEEDED(uri->SchemeIs("ftp", &isFtpURI)) && isFtpURI);
   if (!isFtpURI) {
     return NS_OK;
   }
 
+  // Allow loading FTP subresources in top-level FTP documents.
+  nsIPrincipal* triggeringPrincipal = loadInfo->TriggeringPrincipal();
+  nsCOMPtr<nsIURI> tURI;
+  triggeringPrincipal->GetURI(getter_AddRefs(tURI));
+  bool isTrigFtpURI = (NS_SUCCEEDED(tURI->SchemeIs("ftp", &isTrigFtpURI)) && isTrigFtpURI);
+  if (isTrigFtpURI) {
+    return NS_OK;
+  }
+
+  // If we get here, the request is blocked and should be reported.
   nsCOMPtr<nsIDocument> doc;
   if (nsINode* node = loadInfo->LoadingNode()) {
     doc = node->OwnerDoc();