5 files changed, 25 insertions, 6 deletions

diff --git a/dom/base/nsContentSink.cpp b/dom/base/nsContentSink.cpp
index 1e6465a1b..59f4a9f9a 100644
--- a/dom/base/nsContentSink.cpp
+++ b/dom/base/nsContentSink.cpp
@@ -789,13 +789,14 @@ nsContentSink::ProcessStyleLink(nsIContent* aElement,
   // If this is a fragment parser, we don't want to observe.
   // We don't support CORS for processing instructions
   bool isAlternate;
+  bool isExplicitlyEnabled;
   rv = mCSSLoader->LoadStyleLink(aElement, url, aTitle, aMedia, aAlternate,
                                  CORS_NONE, mDocument->GetReferrerPolicy(),
                                  integrity, mRunsToCompletion ? nullptr : this,
-                                 &isAlternate);
+                                 &isAlternate, &isExplicitlyEnabled);
   NS_ENSURE_SUCCESS(rv, rv);
   
-  if (!isAlternate && !mRunsToCompletion) {
+  if ((!isAlternate || isExplicitlyEnabled) && !mRunsToCompletion) {
     ++mPendingSheetCount;
     mScriptLoader->AddParserBlockingScriptExecutionBlocker();
   }
diff --git a/dom/base/nsDocument.cpp b/dom/base/nsDocument.cpp
index d0634b0f9..de793bfab 100644
--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -12745,3 +12745,16 @@ 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 506acc7e4..29afa5439 100644
--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -2872,6 +2872,8 @@ public:
   virtual void ScheduleIntersectionObserverNotification() = 0;
   virtual void NotifyIntersectionObservers() = 0;
 
+  bool ModuleScriptsEnabled();
+
 protected:
   bool GetUseCounter(mozilla::UseCounter aUseCounter)
   {
diff --git a/dom/base/nsStyleLinkElement.cpp b/dom/base/nsStyleLinkElement.cpp
index 8ab2dab0b..2e5cdac6f 100644
--- a/dom/base/nsStyleLinkElement.cpp
+++ b/dom/base/nsStyleLinkElement.cpp
@@ -393,8 +393,9 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
   nsAutoString title, type, media;
   bool isScoped;
   bool isAlternate;
+  bool isExplicitlyEnabled;
 
-  GetStyleSheetInfo(title, type, media, &isScoped, &isAlternate);
+  GetStyleSheetInfo(title, type, media, &isScoped, &isAlternate, &isExplicitlyEnabled);
 
   if (!type.LowerCaseEqualsLiteral("text/css")) {
     return NS_OK;
@@ -425,7 +426,7 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     // Parse the style sheet.
     rv = doc->CSSLoader()->
       LoadInlineStyle(thisContent, text, mLineNumber, title, media,
-                      scopeElement, aObserver, &doneLoading, &isAlternate);
+                      scopeElement, aObserver, &doneLoading, &isAlternate, &isExplicitlyEnabled);
   }
   else {
     nsAutoString integrity;
@@ -452,13 +453,14 @@ nsStyleLinkElement::DoUpdateStyleSheet(nsIDocument* aOldDocument,
     rv = doc->CSSLoader()->
       LoadStyleLink(thisContent, clonedURI, title, media, isAlternate,
                     GetCORSMode(), referrerPolicy, integrity,
-                    aObserver, &isAlternate);
+                    aObserver, &isAlternate, &isExplicitlyEnabled);
     if (NS_FAILED(rv)) {
       // Don't propagate LoadStyleLink() errors further than this, since some
       // consumers (e.g. nsXMLContentSink) will completely abort on innocuous
       // things like a stylesheet load being blocked by the security system.
       doneLoading = true;
       isAlternate = false;
+      isExplicitlyEnabled = false;
       rv = NS_OK;
     }
   }
diff --git a/dom/base/nsStyleLinkElement.h b/dom/base/nsStyleLinkElement.h
index a41ae5e1d..d9042c756 100644
--- a/dom/base/nsStyleLinkElement.h
+++ b/dom/base/nsStyleLinkElement.h
@@ -98,7 +98,8 @@ protected:
                                  nsAString& aType,
                                  nsAString& aMedia,
                                  bool* aIsScoped,
-                                 bool* aIsAlternate) = 0;
+                                 bool* aIsAlternate,
+                                 bool* aIsExplicitlyEnabled) = 0;
 
   virtual mozilla::CORSMode GetCORSMode() const
   {