Bug 1457389 - Check if extension is in the overflow menu when setting fixedWidth on the popup. r=rpl

MozReview-Commit-ID: 3NqnOMpu18M

--HG--
extra : rebase_source : 2e77701c8e9cf94983b97b4a80d170dd86da0424

browser/components/extensions/parent/ext-browserAction.js

@@ -396,7 +396,9 @@ this.browserAction = class extends ExtensionAPI {
       pendingPopup.destroy();
     }
 
-    let fixedWidth = this.widget.areaType == CustomizableUI.TYPE_MENU_PANEL;
+    let fixedWidth =
+      this.widget.areaType == CustomizableUI.TYPE_MENU_PANEL ||
+      this.widget.forWindow(window).overflowed;
     return new ViewPopup(this.extension, window, popupURL, this.browserStyle, fixedWidth, blockParser);
   }