--- a/editor/libeditor/HTMLEditor.h
+++ b/editor/libeditor/HTMLEditor.h
@@ -197,17 +197,17 @@ public:
   void IsPrevCharInNodeWhitespace(nsIContent* aContent,
                                   int32_t aOffset,
                                   bool* outIsSpace,
                                   bool* outIsNBSP,
                                   nsIContent** outNode = nullptr,
                                   int32_t* outOffset = 0);
 
   // Overrides of EditorBase interface methods
-  nsresult EndUpdateViewBatch() override;
+  virtual nsresult EndUpdateViewBatch() override;
 
   NS_IMETHOD Init(nsIDOMDocument* aDoc, nsIContent* aRoot,
                   nsISelectionController* aSelCon, uint32_t aFlags,
                   const nsAString& aValue) override;
   NS_IMETHOD PreDestroy(bool aDestroyingFrames) override;
 
   /**
    * @param aElement        Must not be null.
@@ -592,22 +592,22 @@ protected:
   nsresult InsertFromTransferable(nsITransferable* transferable,
                                     nsIDOMDocument* aSourceDoc,
                                     const nsAString& aContextStr,
                                     const nsAString& aInfoStr,
                                     bool havePrivateHTMLFlavor,
                                     nsIDOMNode *aDestinationNode,
                                     int32_t aDestinationOffset,
                                     bool aDoDeleteSelection);
-  nsresult InsertFromDataTransfer(dom::DataTransfer* aDataTransfer,
-                                  int32_t aIndex,
-                                  nsIDOMDocument* aSourceDoc,
-                                  nsIDOMNode* aDestinationNode,
-                                  int32_t aDestOffset,
-                                  bool aDoDeleteSelection) override;
+  virtual nsresult InsertFromDataTransfer(dom::DataTransfer* aDataTransfer,
+                                          int32_t aIndex,
+                                          nsIDOMDocument* aSourceDoc,
+                                          nsIDOMNode* aDestinationNode,
+                                          int32_t aDestOffset,
+                                          bool aDoDeleteSelection) override;
   bool HavePrivateHTMLFlavor(nsIClipboard* clipboard );
   nsresult ParseCFHTML(nsCString& aCfhtml, char16_t** aStuffToPaste,
                        char16_t** aCfcontext);
   nsresult DoContentFilterCallback(const nsAString& aFlavor,
                                    nsIDOMDocument* aSourceDoc,
                                    bool aWillDeleteSelection,
                                    nsIDOMNode** aFragmentAsNode,
                                    nsIDOMNode** aFragStartNode,