--- a/docshell/test/navigation/test_bug386782.html
+++ b/docshell/test/navigation/test_bug386782.html
@@ -35,17 +35,17 @@ https://bugzilla.mozilla.org/show_bug.cg
         expectedBodyAfterEdit:  'EDITED <br><p>contentEditable</p>',
         expectedBodyAfterSecondEdit: 'EDITED TWICE <br><p>contentEditable</p>',
       }
     ];
 
     var gTestNum = -1;
     var gTest = null;
 
-    window.onload = goNext();
+    window.onload = goNext;
 
     function goNext() {
       gTestNum++;
       if (gTestNum >= gTests.length) {
         SimpleTest.finish();
         return;
       }
       gTest = gTests[gTestNum];

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -1957,17 +1957,17 @@ public:
     return mLoadedAsInteractiveData;
   }
 
   bool MayStartLayout()
   {
     return mMayStartLayout;
   }
 
-  void SetMayStartLayout(bool aMayStartLayout)
+  virtual void SetMayStartLayout(bool aMayStartLayout)
   {
     mMayStartLayout = aMayStartLayout;
   }
 
   already_AddRefed<nsIDocumentEncoder> GetCachedEncoder();
 
   void SetCachedEncoder(already_AddRefed<nsIDocumentEncoder> aEncoder);
 

--- a/dom/html/nsHTMLDocument.cpp
+++ b/dom/html/nsHTMLDocument.cpp
@@ -2406,17 +2406,17 @@ nsHTMLDocument::GetDesignMode(nsAString&
     aDesignMode.AssignLiteral("off");
   }
   return NS_OK;
 }
 
 void
 nsHTMLDocument::MaybeEditingStateChanged()
 {
-  if (!mPendingMaybeEditingStateChanged &&
+  if (!mPendingMaybeEditingStateChanged && mMayStartLayout &&
       mUpdateNestLevel == 0 && (mContentEditableCount > 0) != IsEditingOn()) {
     if (nsContentUtils::IsSafeToRunScript()) {
       EditingStateChanged();
     } else if (!mInDestructor) {
       nsContentUtils::AddScriptRunner(
         NewRunnableMethod(this, &nsHTMLDocument::MaybeEditingStateChanged));
     }
   }
@@ -2429,16 +2429,25 @@ nsHTMLDocument::EndUpdate(nsUpdateType a
   mPendingMaybeEditingStateChanged = true;
   nsDocument::EndUpdate(aUpdateType);
   if (reset) {
     mPendingMaybeEditingStateChanged = false;
   }
   MaybeEditingStateChanged();
 }
 
+void
+nsHTMLDocument::SetMayStartLayout(bool aMayStartLayout)
+{
+  nsIDocument::SetMayStartLayout(aMayStartLayout);
+
+  MaybeEditingStateChanged();
+}
+
+
 
 // Helper class, used below in ChangeContentEditableCount().
 class DeferredContentEditableCountChangeEvent : public Runnable
 {
 public:
   DeferredContentEditableCountChangeEvent(nsHTMLDocument *aDoc,
                                           nsIContent *aElement)
     : mDoc(aDoc)

--- a/dom/html/nsHTMLDocument.h
+++ b/dom/html/nsHTMLDocument.h
@@ -139,16 +139,18 @@ public:
   private:
     nsHTMLDocument* mDoc;
     EditingState    mSavedState;
   };
   friend class nsAutoEditingState;
 
   void EndUpdate(nsUpdateType aUpdateType) override;
 
+  virtual void SetMayStartLayout(bool aMayStartLayout) override;
+
   virtual nsresult SetEditingState(EditingState aState) override;
 
   virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;
 
   virtual void RemovedFromDocShell() override;
 
   virtual mozilla::dom::Element *GetElementById(const nsAString& aElementId) override
   {