Simple changing Firefox User-Agent using "FF.au3" without manual edit "prefs.js" #Include <FF.au3> If _FFConnect() Then ;Default User-Agent _FFOpenURL("http://useragentstring.com/") Sleep(5000) ;Set new User-Agent FFSetUserAgent("Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/48.0.2564.116 Safari/537.36") _FFOpenURL("http://useragentstring.com/") Sleep(5000)