Issue #1629 - Uplift implementation of <link disabled> behavior for stylesheets.

15 files changed, 123 insertions, 44 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/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
   {
diff --git a/dom/html/HTMLLinkElement.cpp b/dom/html/HTMLLinkElement.cpp
index 8afe767bd..1b78cbd69 100644
--- a/dom/html/HTMLLinkElement.cpp
+++ b/dom/html/HTMLLinkElement.cpp
@@ -33,6 +33,8 @@
 #define LINK_ELEMENT_FLAG_BIT(n_) \
   NODE_FLAG_BIT(ELEMENT_TYPE_SPECIFIC_BITS_OFFSET + (n_))
 
+#define LINK_DISABLED Preferences::GetBool("dom.link.disabled_attribute.enabled", true)
+
 // Link element specific bits
 enum {
   // Indicates that a DNS Prefetch has been requested from this Link element.
@@ -92,9 +94,14 @@ NS_INTERFACE_TABLE_TAIL_INHERITING(nsGenericHTMLElement)
 
 NS_IMPL_ELEMENT_CLONE(HTMLLinkElement)
 
+
 bool
-HTMLLinkElement::Disabled()
+HTMLLinkElement::Disabled() const
 {
+  if (LINK_DISABLED) {
+    return GetBoolAttr(nsGkAtoms::disabled);
+  }
+
   StyleSheet* ss = GetSheet();
   return ss && ss->Disabled();
 }
@@ -107,8 +114,12 @@ HTMLLinkElement::GetMozDisabled(bool* aDisabled)
 }
 
 void
-HTMLLinkElement::SetDisabled(bool aDisabled)
-{
+HTMLLinkElement::SetDisabled(bool aDisabled, ErrorResult& aRv)
+{ 
+  if (LINK_DISABLED) {
+  return SetHTMLBoolAttr(nsGkAtoms::disabled, aDisabled, aRv);
+  }
+
   if (StyleSheet* ss = GetSheet()) {
     ss->SetDisabled(aDisabled);
   }
@@ -117,11 +128,11 @@ HTMLLinkElement::SetDisabled(bool aDisabled)
 NS_IMETHODIMP
 HTMLLinkElement::SetMozDisabled(bool aDisabled)
 {
-  SetDisabled(aDisabled);
-  return NS_OK;
+  ErrorResult rv;
+  SetDisabled(aDisabled, rv);
+  return rv.StealNSResult(); 
 }
 
-
 NS_IMPL_STRING_ATTR(HTMLLinkElement, Charset, charset)
 NS_IMPL_URI_ATTR(HTMLLinkElement, Href, href)
 NS_IMPL_STRING_ATTR(HTMLLinkElement, Hreflang, hreflang)
@@ -369,7 +380,8 @@ HTMLLinkElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
          aName == nsGkAtoms::rel ||
          aName == nsGkAtoms::title ||
          aName == nsGkAtoms::media ||
-         aName == nsGkAtoms::type)) {
+         aName == nsGkAtoms::type ||
+         (LINK_DISABLED && aName == nsGkAtoms::disabled))) {
       bool dropSheet = false;
       if (aName == nsGkAtoms::rel) {
         nsAutoString value;
@@ -396,17 +408,24 @@ HTMLLinkElement::AfterSetAttr(int32_t aNameSpaceID, nsIAtom* aName,
                                dropSheet ||
                                (aName == nsGkAtoms::title ||
                                 aName == nsGkAtoms::media ||
-                                aName == nsGkAtoms::type));
+                                aName == nsGkAtoms::type ||
+                                (LINK_DISABLED && aName == nsGkAtoms::disabled)));
     }
   } else {
-    // Since removing href or rel makes us no longer link to a
-    // stylesheet, force updates for those too.
+    // If the disabled attribute is removed from a link element, the 
+    // stylesheet may be explicitly enabled.
     if (aNameSpaceID == kNameSpaceID_None) {
+      if (aName == nsGkAtoms::disabled && LINK_DISABLED) {
+        mExplicitlyEnabled = true;
+      }
+      // Since removing href or rel makes us no longer link to a
+      // stylesheet, force updates for those too.
       if (aName == nsGkAtoms::href ||
           aName == nsGkAtoms::rel ||
           aName == nsGkAtoms::title ||
           aName == nsGkAtoms::media ||
-          aName == nsGkAtoms::type) {
+          aName == nsGkAtoms::type ||
+          (LINK_DISABLED && aName == nsGkAtoms::disabled)) {
         UpdateStyleSheetInternal(nullptr, nullptr, true);
       }
       if (aName == nsGkAtoms::href ||
@@ -499,13 +518,15 @@ HTMLLinkElement::GetStyleSheetInfo(nsAString& aTitle,
                                    nsAString& aType,
                                    nsAString& aMedia,
                                    bool* aIsScoped,
-                                   bool* aIsAlternate)
+                                   bool* aIsAlternate,
+                                   bool* aIsExplicitlyEnabled)
 {
   aTitle.Truncate();
   aType.Truncate();
   aMedia.Truncate();
   *aIsScoped = false;
   *aIsAlternate = false;
+  *aIsExplicitlyEnabled = false;
 
   nsAutoString rel;
   GetAttr(kNameSpaceID_None, nsGkAtoms::rel, rel);
@@ -515,6 +536,20 @@ HTMLLinkElement::GetStyleSheetInfo(nsAString& aTitle,
     return;
   }
 
+  if (LINK_DISABLED) {
+
+  // Is the link disabled?
+  if (Disabled()) {
+    return;
+  }
+
+  // Is it explicitly enabled?
+  if (mExplicitlyEnabled) {
+    *aIsExplicitlyEnabled = true;
+  }
+
+  }
+
   nsAutoString title;
   GetAttr(kNameSpaceID_None, nsGkAtoms::title, title);
   title.CompressWhitespace();
diff --git a/dom/html/HTMLLinkElement.h b/dom/html/HTMLLinkElement.h
index 421b149e9..f9c832c8d 100644
--- a/dom/html/HTMLLinkElement.h
+++ b/dom/html/HTMLLinkElement.h
@@ -84,8 +84,8 @@ public:
   virtual bool HasDeferredDNSPrefetchRequest() override;
 
   // WebIDL
-  bool Disabled();
-  void SetDisabled(bool aDisabled);
+  bool Disabled() const;
+  void SetDisabled(bool aDisabled, ErrorResult& aRv);
   // XPCOM GetHref is fine.
   void SetHref(const nsAString& aHref, ErrorResult& aRv)
   {
@@ -179,10 +179,18 @@ protected:
                                  nsAString& aType,
                                  nsAString& aMedia,
                                  bool* aIsScoped,
-                                 bool* aIsAlternate) override;
-protected:
+                                 bool* aIsAlternate,
+                                 bool* aIsExplicitlyEnabled) override;
+
   RefPtr<nsDOMTokenList> mRelList;
 
+  // The "explicitly enabled" flag. This flag is set whenever the 'disabled'
+  // attribute is explicitly unset, and makes alternate stylesheets not be
+  // disabled by default anymore.
+  //
+  // See https://github.com/whatwg/html/issues/3840#issuecomment-481034206.
+  bool mExplicitlyEnabled = false;
+
 private:
   RefPtr<ImportLoader> mImportLoader;
 };
diff --git a/dom/html/HTMLStyleElement.cpp b/dom/html/HTMLStyleElement.cpp
index 329dda648..87dc68f83 100644
--- a/dom/html/HTMLStyleElement.cpp
+++ b/dom/html/HTMLStyleElement.cpp
@@ -66,7 +66,7 @@ HTMLStyleElement::GetMozDisabled(bool* aDisabled)
 }
 
 bool
-HTMLStyleElement::Disabled()
+HTMLStyleElement::Disabled() const
 {
   StyleSheet* ss = GetSheet();
   return ss && ss->Disabled();
@@ -222,12 +222,14 @@ HTMLStyleElement::GetStyleSheetInfo(nsAString& aTitle,
                                     nsAString& aType,
                                     nsAString& aMedia,
                                     bool* aIsScoped,
-                                    bool* aIsAlternate)
+                                    bool* aIsAlternate,
+                                    bool* aIsExplicitlyEnabled)
 {
   aTitle.Truncate();
   aType.Truncate();
   aMedia.Truncate();
   *aIsAlternate = false;
+  *aIsExplicitlyEnabled = false;
 
   nsAutoString title;
   GetAttr(kNameSpaceID_None, nsGkAtoms::title, title);
diff --git a/dom/html/HTMLStyleElement.h b/dom/html/HTMLStyleElement.h
index 6b2a12b1f..9f82b8e51 100644
--- a/dom/html/HTMLStyleElement.h
+++ b/dom/html/HTMLStyleElement.h
@@ -58,7 +58,7 @@ public:
   NS_DECL_NSIMUTATIONOBSERVER_CONTENTINSERTED
   NS_DECL_NSIMUTATIONOBSERVER_CONTENTREMOVED
 
-  bool Disabled();
+  bool Disabled() const;
   void SetDisabled(bool aDisabled);
   void SetMedia(const nsAString& aMedia, ErrorResult& aError)
   {
@@ -87,7 +87,8 @@ protected:
                          nsAString& aType,
                          nsAString& aMedia,
                          bool* aIsScoped,
-                         bool* aIsAlternate) override;
+                         bool* aIsAlternate,
+                         bool* aIsExplicitlyEnabled) override;
   /**
    * Common method to call from the various mutation observer methods.
    * aContent is a content node that's either the one that changed or its
diff --git a/dom/svg/SVGStyleElement.cpp b/dom/svg/SVGStyleElement.cpp
index 22fb204df..7655c1198 100644
--- a/dom/svg/SVGStyleElement.cpp
+++ b/dom/svg/SVGStyleElement.cpp
@@ -271,9 +271,11 @@ SVGStyleElement::GetStyleSheetInfo(nsAString& aTitle,
                                    nsAString& aType,
                                    nsAString& aMedia,
                                    bool* aIsScoped,
-                                   bool* aIsAlternate)
+                                   bool* aIsAlternate,
+                                   bool* aIsExplicitlyEnabled)
 {
   *aIsAlternate = false;
+  *aIsExplicitlyEnabled = false;
 
   nsAutoString title;
   GetAttr(kNameSpaceID_None, nsGkAtoms::title, title);
diff --git a/dom/svg/SVGStyleElement.h b/dom/svg/SVGStyleElement.h
index 9b126e7e8..e637dfb18 100644
--- a/dom/svg/SVGStyleElement.h
+++ b/dom/svg/SVGStyleElement.h
@@ -95,7 +95,8 @@ protected:
                          nsAString& aType,
                          nsAString& aMedia,
                          bool* aIsScoped,
-                         bool* aIsAlternate) override;
+                         bool* aIsAlternate,
+                         bool* aIsExplicitlyEnabled) override;
   virtual CORSMode GetCORSMode() const override;
 
   /**
diff --git a/dom/webidl/HTMLLinkElement.webidl b/dom/webidl/HTMLLinkElement.webidl
index ec094e55e..0b77e9ea7 100644
--- a/dom/webidl/HTMLLinkElement.webidl
+++ b/dom/webidl/HTMLLinkElement.webidl
@@ -13,7 +13,7 @@
 
 // http://www.whatwg.org/specs/web-apps/current-work/#the-link-element
 interface HTMLLinkElement : HTMLElement {
-  [Pure]
+  [CEReactions, SetterThrows, Pure]
            attribute boolean disabled;
   [SetterThrows, Pure]
            attribute DOMString href;
diff --git a/dom/xml/XMLStylesheetProcessingInstruction.cpp b/dom/xml/XMLStylesheetProcessingInstruction.cpp
index 3d94e179b..43e45131a 100644
--- a/dom/xml/XMLStylesheetProcessingInstruction.cpp
+++ b/dom/xml/XMLStylesheetProcessingInstruction.cpp
@@ -131,13 +131,15 @@ XMLStylesheetProcessingInstruction::GetStyleSheetInfo(nsAString& aTitle,
                                                       nsAString& aType,
                                                       nsAString& aMedia,
                                                       bool* aIsScoped,
-                                                      bool* aIsAlternate)
+                                                      bool* aIsAlternate,
+                                                      bool* aIsExplicitlyEnabled)
 {
   aTitle.Truncate();
   aType.Truncate();
   aMedia.Truncate();
   *aIsScoped = false;
   *aIsAlternate = false;
+  *aIsExplicitlyEnabled = false;
 
   // xml-stylesheet PI is special only in prolog
   if (!nsContentUtils::InProlog(this)) {
diff --git a/dom/xml/XMLStylesheetProcessingInstruction.h b/dom/xml/XMLStylesheetProcessingInstruction.h
index 818b3392f..28061834a 100644
--- a/dom/xml/XMLStylesheetProcessingInstruction.h
+++ b/dom/xml/XMLStylesheetProcessingInstruction.h
@@ -82,7 +82,8 @@ protected:
                          nsAString& aType,
                          nsAString& aMedia,
                          bool* aIsScoped,
-                         bool* aIsAlternate) override;
+                         bool* aIsAlternate,
+                         bool* aIsExplicitlyEnabled) override;
   virtual nsGenericDOMDataNode* CloneDataNode(mozilla::dom::NodeInfo *aNodeInfo,
                                               bool aCloneText) const override;
 };
diff --git a/layout/style/Loader.cpp b/layout/style/Loader.cpp
index 0ce337e29..df523174d 100644
--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -1277,7 +1277,8 @@ Loader::PrepareSheet(StyleSheet* aSheet,
                      const nsSubstring& aMediaString,
                      nsMediaList* aMediaList,
                      Element* aScopeElement,
-                     bool isAlternate)
+                     bool isAlternate,
+                     bool isExplicitlyEnabled)
 {
   NS_PRECONDITION(aSheet, "Must have a sheet!");
 
@@ -1306,7 +1307,7 @@ Loader::PrepareSheet(StyleSheet* aSheet,
   sheet->SetMedia(mediaList);
 
   sheet->SetTitle(aTitle);
-  sheet->SetEnabled(!isAlternate);
+  sheet->SetEnabled(!isAlternate || isExplicitlyEnabled);
   sheet->SetScopeElement(aScopeElement);
 }
 
@@ -1984,7 +1985,8 @@ Loader::LoadInlineStyle(nsIContent* aElement,
                         Element* aScopeElement,
                         nsICSSLoaderObserver* aObserver,
                         bool* aCompleted,
-                        bool* aIsAlternate)
+                        bool* aIsAlternate,
+                        bool* aIsExplicitlyEnabled)
 {
   LOG(("css::Loader::LoadInlineStyle"));
   NS_ASSERTION(mParsingDatas.Length() == 0, "We're in the middle of a parse?");
@@ -2016,8 +2018,9 @@ Loader::LoadInlineStyle(nsIContent* aElement,
                "Inline sheets should not be cached");
 
   LOG(("  Sheet is alternate: %d", *aIsAlternate));
+  LOG(("  Sheet is explicitly enabled: %d", *aIsExplicitlyEnabled));
 
-  PrepareSheet(sheet, aTitle, aMedia, nullptr, aScopeElement, *aIsAlternate);
+  PrepareSheet(sheet, aTitle, aMedia, nullptr, aScopeElement, *aIsAlternate, *aIsExplicitlyEnabled);
 
   if (aElement->HasFlag(NODE_IS_IN_SHADOW_TREE)) {
     ShadowRoot* containingShadow = aElement->GetContainingShadow();
@@ -2058,7 +2061,8 @@ Loader::LoadStyleLink(nsIContent* aElement,
                       ReferrerPolicy aReferrerPolicy,
                       const nsAString& aIntegrity,
                       nsICSSLoaderObserver* aObserver,
-                      bool* aIsAlternate)
+                      bool* aIsAlternate,
+                      bool* aIsExplicitlyEnabled)
 {
   LOG(("css::Loader::LoadStyleLink"));
   NS_PRECONDITION(aURL, "Must have URL to load");
@@ -2111,8 +2115,9 @@ Loader::LoadStyleLink(nsIContent* aElement,
   NS_ENSURE_SUCCESS(rv, rv);
 
   LOG(("  Sheet is alternate: %d", *aIsAlternate));
+  LOG(("  Sheet is explicitly enabled: %d", *aIsExplicitlyEnabled));
 
-  PrepareSheet(sheet, aTitle, aMedia, nullptr, nullptr, *aIsAlternate);
+  PrepareSheet(sheet, aTitle, aMedia, nullptr, nullptr, *aIsAlternate, *aIsExplicitlyEnabled);
 
   rv = InsertSheetInDoc(sheet, aElement, mDocument);
   NS_ENSURE_SUCCESS(rv, rv);
@@ -2137,9 +2142,10 @@ Loader::LoadStyleLink(nsIContent* aElement,
                                           aObserver, principal, requestingNode);
   NS_ADDREF(data);
 
-  // If we have to parse and it's an alternate non-inline, defer it
+  // If we have to parse and it's an alternate non-inline, defer it unless
+  // it's explicitly enabled.
   if (aURL && state == eSheetNeedsParser && mSheets->mLoadingDatas.Count() != 0 &&
-      *aIsAlternate) {
+      *aIsAlternate && !*aIsExplicitlyEnabled) {
     LOG(("  Deferring alternate sheet load"));
     URIPrincipalReferrerPolicyAndCORSModeHashKey key(data->mURI,
                                                      data->mLoaderPrincipal,
@@ -2266,6 +2272,7 @@ Loader::LoadChildSheet(StyleSheet* aParentSheet,
     state = eSheetComplete;
   } else {
     bool isAlternate;
+    bool isExplicitlyEnabled;
     const nsSubstring& empty = EmptyString();
     // For now, use CORS_NONE for child sheets
     rv = CreateSheet(aURL, nullptr, principal,
@@ -2276,7 +2283,7 @@ Loader::LoadChildSheet(StyleSheet* aParentSheet,
                      false, empty, state, &isAlternate, &sheet);
     NS_ENSURE_SUCCESS(rv, rv);
 
-    PrepareSheet(sheet, empty, empty, aMedia, nullptr, isAlternate);
+    PrepareSheet(sheet, empty, empty, aMedia, nullptr, isAlternate, isExplicitlyEnabled);
   }
 
   rv = InsertChildSheet(sheet, aParentSheet, aParentRule);
@@ -2389,6 +2396,7 @@ Loader::InternalLoadNonDocumentSheet(nsIURI* aURL,
 
   StyleSheetState state;
   bool isAlternate;
+  bool isExplicitlyEnabled;
   RefPtr<StyleSheet> sheet;
   bool syncLoad = (aObserver == nullptr);
   const nsSubstring& empty = EmptyString();
@@ -2398,7 +2406,7 @@ Loader::InternalLoadNonDocumentSheet(nsIURI* aURL,
                    false, empty, state, &isAlternate, &sheet);
   NS_ENSURE_SUCCESS(rv, rv);
 
-  PrepareSheet(sheet, empty, empty, nullptr, nullptr, isAlternate);
+  PrepareSheet(sheet, empty, empty, nullptr, nullptr, isAlternate, isExplicitlyEnabled);
 
   if (state == eSheetComplete) {
     LOG(("  Sheet already complete"));
diff --git a/layout/style/Loader.h b/layout/style/Loader.h
index 209783a80..4a3088b6b 100644
--- a/layout/style/Loader.h
+++ b/layout/style/Loader.h
@@ -230,6 +230,8 @@ public:
    * @param [out] aCompleted whether parsing of the sheet completed.
    * @param [out] aIsAlternate whether the stylesheet ended up being an
    *        alternate sheet.
+   * @param [out] aIsExplicitlyEnabled whether the stylesheet was explicitly
+   *        enabled by having the disabled attribute removed. 
    */
   nsresult LoadInlineStyle(nsIContent* aElement,
                            const nsAString& aBuffer,
@@ -239,7 +241,8 @@ public:
                            mozilla::dom::Element* aScopeElement,
                            nsICSSLoaderObserver* aObserver,
                            bool* aCompleted,
-                           bool* aIsAlternate);
+                           bool* aIsAlternate,
+			   bool* aIsExplicitlyEnabled);
 
   /**
    * Load a linked (document) stylesheet.  If a successful result is returned,
@@ -260,6 +263,8 @@ public:
    * @param [out] aIsAlternate whether the stylesheet actually ended up beinga
    *        an alternate sheet.  Note that this need not match
    *        aHasAlternateRel.
+   * @param [out] aIsExplicitlyEnabled whether the stylesheet was explicitly
+   *        enabled by having the disabled attribute removed.
    */
   nsresult LoadStyleLink(nsIContent* aElement,
                          nsIURI* aURL,
@@ -270,7 +275,8 @@ public:
                          ReferrerPolicy aReferrerPolicy,
                          const nsAString& aIntegrity,
                          nsICSSLoaderObserver* aObserver,
-                         bool* aIsAlternate);
+                         bool* aIsAlternate,
+			 bool* aIsExplicitlyEnabled);
 
   /**
    * Load a child (@import-ed) style sheet.  In addition to loading the sheet,
@@ -476,7 +482,8 @@ private:
                     const nsAString& aMediaString,
                     nsMediaList* aMediaList,
                     dom::Element* aScopeElement,
-                    bool isAlternate);
+                    bool isAlternate,
+		    bool isExplicitlyEnabled);
 
   nsresult InsertSheetInDoc(StyleSheet* aSheet,
                             nsIContent* aLinkingContent,
diff --git a/modules/libpref/init/all.js b/modules/libpref/init/all.js
index 60851e55e..7dbeec54a 100644
--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -1185,6 +1185,14 @@ pref("dom.storage.default_quota",      5120);
 
 pref("dom.send_after_paint_to_content", false);
 
+// Whether the disabled attribute in HTMLLinkElement disables the sheet loading
+// altogether, or forwards to the inner stylesheet method without attribute
+// reflection.
+//
+// Historical behavior is the second, the first is being discussed at:
+// https://github.com/whatwg/html/issues/3840
+pref("dom.link.disabled_attribute.enabled", true);
+
 // Timeout clamp in ms for timeouts we clamp
 pref("dom.min_timeout_value", 4);
 // And for background windows