diff --git a/dom/base/nsGlobalWindow.h b/dom/base/nsGlobalWindow.h
index 0cee12bfea5d..508013879fb7 100644
--- a/dom/base/nsGlobalWindow.h
+++ b/dom/base/nsGlobalWindow.h
@@ -434,7 +434,6 @@ public:
   {
     return mIsFrozen;
   }
-  virtual NS_HIDDEN_(bool) IsRunningTimeout() { return mTimeoutFiringDepth > 0; }
 
   virtual NS_HIDDEN_(bool) WouldReuseInnerWindow(nsIDocument *aNewDocument);
 
diff --git a/dom/base/nsPIDOMWindow.h b/dom/base/nsPIDOMWindow.h
index 45f524d779fa..580e420848a3 100644
--- a/dom/base/nsPIDOMWindow.h
+++ b/dom/base/nsPIDOMWindow.h
@@ -189,8 +189,6 @@ public:
     return mDoc;
   }
 
-  virtual NS_HIDDEN_(bool) IsRunningTimeout() = 0;
-
 protected:
   // Lazily instantiate an about:blank document if necessary, and if
   // we have what it takes to do so.