--- a/browser/components/extensions/parent/ext-browserAction.js
+++ b/browser/components/extensions/parent/ext-browserAction.js
@@ -391,17 +391,19 @@ this.browserAction = class extends Exten
           pendingPopup.unblockParser();
         }
 
         return pendingPopup;
       }
       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);
   }
 
   /**
    * Clears any pending pre-loaded popup and related timeouts.
    */
   clearPopup() {
     this.clearPopupTimeout();