--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -595,29 +595,19 @@ CSSStyleSheet::UseForPresentation(nsPres
 
 bool
 CSSStyleSheet::HasRules() const
 {
   return StyleRuleCount() != 0;
 }
 
 void
-CSSStyleSheet::SetEnabled(bool aEnabled)
+CSSStyleSheet::EnabledStateChangedInternal()
 {
-  // Internal method, so callers must handle BeginUpdate/EndUpdate
-  bool oldDisabled = mDisabled;
-  mDisabled = !aEnabled;
-
-  if (mInner->mComplete && oldDisabled != mDisabled) {
-    ClearRuleCascades();
-
-    if (mDocument) {
-      mDocument->SetStyleSheetApplicableState(this, !mDisabled);
-    }
-  }
+  ClearRuleCascades();
 }
 
 CSSStyleSheet*
 CSSStyleSheet::GetParentSheet() const
 {
   return mParent;
 }
 

--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -110,27 +110,16 @@ public:
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(CSSStyleSheet, StyleSheet)
 
   NS_DECLARE_STATIC_IID_ACCESSOR(NS_CSS_STYLE_SHEET_IMPL_CID)
 
   bool HasRules() const;
 
-  /**
-   * Set the stylesheet to be enabled.  This may or may not make it
-   * applicable.  Note that this WILL inform the sheet's document of
-   * its new applicable state if the state changes but WILL NOT call
-   * BeginUpdate() or EndUpdate() on the document -- calling those is
-   * the caller's responsibility.  This allows use of SetEnabled when
-   * batched updates are desired.  If you want updates handled for
-   * you, see nsIDOMStyleSheet::SetDisabled().
-   */
-  void SetEnabled(bool aEnabled);
-
   // style sheet owner info
   CSSStyleSheet* GetParentSheet() const;  // may be null
   void SetOwningDocument(nsIDocument* aDocument);
 
   // Find the ID of the owner inner window.
   uint64_t FindOwningWindowInnerID() const;
 #ifdef DEBUG
   void List(FILE* out = stdout, int32_t aIndent = 0) const;
@@ -238,16 +227,18 @@ protected:
 
 protected:
   // Internal methods which do not have security check and completeness check.
   dom::CSSRuleList* GetCssRulesInternal(ErrorResult& aRv);
   uint32_t InsertRuleInternal(const nsAString& aRule,
                               uint32_t aIndex, ErrorResult& aRv);
   void DeleteRuleInternal(uint32_t aIndex, ErrorResult& aRv);
 
+  void EnabledStateChangedInternal();
+
   RefPtr<CSSStyleSheet> mNext;
   CSSStyleSheet*        mParent;    // weak ref
   css::ImportRule*      mOwnerRule; // weak ref
 
   RefPtr<CSSRuleListImpl> mRuleCollection;
   bool                  mDirty; // has been modified 
   bool                  mInRuleProcessorCache;
   RefPtr<dom::Element> mScopeElement;

--- a/layout/style/Loader.cpp
+++ b/layout/style/Loader.cpp
@@ -1302,17 +1302,17 @@ Loader::PrepareSheet(StyleSheet* aSheet,
     // We have aMediaString only when linked from link elements, style
     // elements, or PIs, so pass true.
     mediumParser.ParseMediaList(aMediaString, nullptr, 0, mediaList);
   }
 
   aSheet->SetMedia(mediaList);
 
   aSheet->SetTitle(aTitle);
-  sheet->SetEnabled(!aIsAlternate);
+  aSheet->SetEnabled(!aIsAlternate);
   sheet->SetScopeElement(aScopeElement);
 }
 
 /**
  * InsertSheetInDoc handles ordering of sheets in the document.  Here
  * we have two types of sheets -- those with linking elements and
  * those without.  The latter are loaded by Link: headers.
  * The following constraints are observed:

--- a/layout/style/ServoStyleSheet.h
+++ b/layout/style/ServoStyleSheet.h
@@ -79,16 +79,18 @@ protected:
   virtual ~ServoStyleSheet();
 
   // Internal methods which do not have security check and completeness check.
   dom::CSSRuleList* GetCssRulesInternal(ErrorResult& aRv);
   uint32_t InsertRuleInternal(const nsAString& aRule,
                               uint32_t aIndex, ErrorResult& aRv);
   void DeleteRuleInternal(uint32_t aIndex, ErrorResult& aRv);
 
+  void EnabledStateChangedInternal() {}
+
 private:
   void DropSheet();
 
   RefPtr<RawServoStyleSheet> mSheet;
   RefPtr<ServoCSSRuleList> mRuleList;
   StyleSheetInfo mSheetInfo;
 
   friend class StyleSheet;

--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -113,16 +113,32 @@ StyleSheet::SetComplete()
   if (mOwningNode && !mDisabled &&
       mOwningNode->HasFlag(NODE_IS_IN_SHADOW_TREE) &&
       mOwningNode->IsContent()) {
     dom::ShadowRoot* shadowRoot = mOwningNode->AsContent()->GetContainingShadow();
     shadowRoot->StyleSheetChanged();
   }
 }
 
+void
+StyleSheet::SetEnabled(bool aEnabled)
+{
+  // Internal method, so callers must handle BeginUpdate/EndUpdate
+  bool oldDisabled = mDisabled;
+  mDisabled = !aEnabled;
+
+  if (IsComplete() && oldDisabled != mDisabled) {
+    EnabledStateChanged();
+
+    if (mDocument) {
+      mDocument->SetStyleSheetApplicableState(this, !mDisabled);
+    }
+  }
+}
+
 StyleSheetInfo::StyleSheetInfo(CORSMode aCORSMode,
                                ReferrerPolicy aReferrerPolicy,
                                const dom::SRIMetadata& aIntegrity)
   : mPrincipal(nsNullPrincipal::Create())
   , mCORSMode(aCORSMode)
   , mReferrerPolicy(aReferrerPolicy)
   , mIntegrity(aIntegrity)
   , mComplete(false)
@@ -280,16 +296,22 @@ StyleSheet::DeleteRule(uint32_t aIndex,
                        ErrorResult& aRv)
 {
   if (!AreRulesAvailable(aSubjectPrincipal, aRv)) {
     return;
   }
   FORWARD_INTERNAL(DeleteRuleInternal, (aIndex, aRv))
 }
 
+void
+StyleSheet::EnabledStateChanged()
+{
+  FORWARD_INTERNAL(EnabledStateChangedInternal, ())
+}
+
 #undef FORWARD_INTERNAL
 
 void
 StyleSheet::SubjectSubsumesInnerPrincipal(nsIPrincipal& aSubjectPrincipal,
                                           ErrorResult& aRv)
 {
   StyleSheetInfo& info = SheetInfo();
 

--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -62,16 +62,27 @@ public:
   nsIDocument* GetDocument() const { return mDocument; }
 
   /**
    * Whether the sheet is complete.
    */
   bool IsComplete() const;
   void SetComplete();
 
+  /**
+   * Set the stylesheet to be enabled.  This may or may not make it
+   * applicable.  Note that this WILL inform the sheet's document of
+   * its new applicable state if the state changes but WILL NOT call
+   * BeginUpdate() or EndUpdate() on the document -- calling those is
+   * the caller's responsibility.  This allows use of SetEnabled when
+   * batched updates are desired.  If you want updates handled for
+   * you, see nsIDOMStyleSheet::SetDisabled().
+   */
+  void SetEnabled(bool aEnabled);
+
   MOZ_DECL_STYLO_METHODS(CSSStyleSheet, ServoStyleSheet)
 
   // Whether the sheet is for an inline <style> element.
   inline bool IsInline() const;
 
   inline nsIURI* GetSheetURI() const;
   /* Get the URI this sheet was originally loaded from, if any.  Can
      return null */
@@ -193,16 +204,19 @@ protected:
   // UniversalXPConnect or if access is allowed by CORS.  In the latter case,
   // it will set the principal of the inner to the subject principal.
   void SubjectSubsumesInnerPrincipal(nsIPrincipal& aSubjectPrincipal,
                                      ErrorResult& aRv);
 
   // Drop our reference to mMedia
   void DropMedia();
 
+  // Called from SetEnabled when the enabled state changed.
+  void EnabledStateChanged();
+
   nsString              mTitle;
   nsIDocument*          mDocument; // weak ref; parents maintain this for their children
   nsINode*              mOwningNode; // weak ref
 
   RefPtr<nsMediaList> mMedia;
 
   // mParsingMode controls access to nonstandard style constructs that
   // are not safe for use on the public Web but necessary in UA sheets