Bug 1704569 - Don't synthesize events on menus in...

Bug 1704569 - Don't synthesize events on menus in dom/html/test/browser_content_contextmenu_userinput.js. r=saschanaz

Differential Revision: https://phabricator.services.mozilla.com/D111774

dom/html/test/browser_content_contextmenu_userinput.js

@@ -65,7 +65,7 @@ add_task(async function() {
           });
         }
       );
-      EventUtils.synthesizeMouseAtCenter(testMenuItem, {}, window);
+      contextMenu.activateItem(testMenuItem);
       await promiseCtxMenuClick;
     }
   );