--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -3205,18 +3205,18 @@ public:
     return !mIntersectionObservers.IsEmpty();
   }
 
   void UpdateIntersectionObservations();
   void ScheduleIntersectionObserverNotification();
   void NotifyIntersectionObservers();
 
   // Dispatch a runnable related to the document.
-  virtual nsresult Dispatch(mozilla::TaskCategory aCategory,
-                            already_AddRefed<nsIRunnable>&& aRunnable) override;
+  nsresult Dispatch(mozilla::TaskCategory aCategory,
+                    already_AddRefed<nsIRunnable>&& aRunnable) final;
 
   virtual nsISerialEventTarget*
   EventTargetFor(mozilla::TaskCategory aCategory) const override;
 
   virtual mozilla::AbstractThread*
   AbstractMainThreadFor(mozilla::TaskCategory aCategory) override;
 
   // The URLs passed to these functions should match what