Rated 5 out of 5 stars

Hi, I put opacity to 0% but now I can't see windows anymore Please help !

Open the firefox, then press `CTRL + ARROR_RIGHT`.

If the above operation is invalid, you can open the firefox profile directory(see http://kb.mozillazine.org/Profile_folder_-_Firefox), make sure your firefox is closed, then edit the `pref.js` file, find `extensions.TrayHotKey.opacity_int`, and change its value to 255 (see http://kb.mozillazine.org/User.js_file), then save and reopen firefox.