diff --git a/mozilla/embedding/components/windowwatcher/public/nsIWindowWatcher.idl b/mozilla/embedding/components/windowwatcher/public/nsIWindowWatcher.idl
index cebe85214ab..28900cf81a9 100644
--- a/mozilla/embedding/components/windowwatcher/public/nsIWindowWatcher.idl
+++ b/mozilla/embedding/components/windowwatcher/public/nsIWindowWatcher.idl
@@ -96,6 +96,8 @@ interface nsIWindowWatcher : nsISupports {
       @note This method should try to set the default charset for the new
             window to the default charset of aParent.  This is not guaranteed,
             however.
+      @note This method may dispatch a "toplevel-window-ready" notification
+            via nsIObserverService if the window did not already exist.
   */
   nsIDOMWindow openWindow(in nsIDOMWindow aParent, in string aUrl,
                in string aName, in string aFeatures,
diff --git a/mozilla/embedding/components/windowwatcher/src/nsWindowWatcher.cpp b/mozilla/embedding/components/windowwatcher/src/nsWindowWatcher.cpp
index b52e4aa24a4..c2e14b866ad 100644
--- a/mozilla/embedding/components/windowwatcher/src/nsWindowWatcher.cpp
+++ b/mozilla/embedding/components/windowwatcher/src/nsWindowWatcher.cpp
@@ -839,6 +839,16 @@ nsWindowWatcher::OpenWindowJSInternal(nsIDOMWindow *aParent,
     }
   }
 
+  if (windowIsNew) {
+    // Notify observers that the window is open and ready.
+    // The window has not yet started to load a document.
+    nsCOMPtr<nsIObserverService> obsSvc =
+      do_GetService("@mozilla.org/observer-service;1");
+    if (obsSvc) {
+      obsSvc->NotifyObservers(*_retval, "toplevel-window-ready", nsnull);
+    }
+  }
+
   if (uriToLoad) { // get the script principal and pass it to docshell
     JSContextAutoPopper contextGuard;