diff --git a/mozilla/content/base/src/nsDocument.h b/mozilla/content/base/src/nsDocument.h
index 8ae051c7dea..00e224e298c 100644
--- a/mozilla/content/base/src/nsDocument.h
+++ b/mozilla/content/base/src/nsDocument.h
@@ -618,8 +618,8 @@ public:
                                    const nsIID& aIID);
   NS_IMETHOD RemoveEventListenerByIID(nsIDOMEventListener *aListener,
                                       const nsIID& aIID);
-  NS_IMETHOD GetListenerManager(PRBool aCreateIfNotFound,
-                                nsIEventListenerManager** aResult);
+  virtual nsresult GetListenerManager(PRBool aCreateIfNotFound,
+                                      nsIEventListenerManager** aResult);
   NS_IMETHOD HandleEvent(nsIDOMEvent *aEvent);
   NS_IMETHOD GetSystemEventGroup(nsIDOMEventGroup** aGroup);