--- a/browser/components/customizableui/content/panelUI.js
+++ b/browser/components/customizableui/content/panelUI.js
@@ -178,16 +178,21 @@ const PanelUI = {
     if (document.documentElement.hasAttribute("customizing")) {
       return;
     }
 
     this.panel.hidePopup();
   },
 
   handleEvent: function(aEvent) {
+    // Ignore context menus and menu button menus showing and hiding:
+    if (aEvent.type.startsWith("popup") &&
+        aEvent.target != this.panel) {
+      return;
+    }
     switch (aEvent.type) {
       case "popupshowing":
         this._adjustLabelsForAutoHyphens();
         // Fall through
       case "popupshown":
         // Fall through
       case "popuphiding":
         // Fall through