diff --git a/mozilla/layout/xul/base/src/nsXULPopupManager.cpp b/mozilla/layout/xul/base/src/nsXULPopupManager.cpp
index 216df6732e7..b462a8e2dab 100644
--- a/mozilla/layout/xul/base/src/nsXULPopupManager.cpp
+++ b/mozilla/layout/xul/base/src/nsXULPopupManager.cpp
@@ -934,6 +934,10 @@ nsXULPopupManager::FirePopupShowingEvent(nsIContent* aPopup,
 {
   nsCOMPtr<nsIPresShell> presShell = aPresContext->PresShell();
 
+  if (aMenu)
+    aMenu->SetAttr(kNameSpaceID_None, nsGkAtoms::open,
+                   NS_LITERAL_STRING("true"), PR_TRUE);
+
   // XXXndeakin (bug 383930)
   //   eventually, the popup events will be a different event type with
   //   additional fields for the anchor node and position and so forth. This