User Agent: Mozilla/5.0 (Windows NT 6.1; '''WOW64'''; rv:41.0) Gecko/20100101 Firefox/41.0 Your useragent shows it is a 32-bit Firefox on 64-bit Windows with the WOW64. Firefox 42.0 released yesterday is the first Release to have Win64 along with 32-bit for Windows. However the Win64 is not so visible as it is currently not being listed on www.mozilla.org or www.mozilla.org/firefox/all You can download it from links like below where you pick your language. https://archive.mozilla.org/pub/firefox/releases/latest/win64/ https://ftp.mozilla.org/pub/firefox/releases/latest/win64/ http://download-origin.cdn.mozilla.net/pub/firefox/releases/latest/win64/ Do note that the only 64-bit Plugin (on Windows) that will run on Win64 Firefox is the Flash Player plugin currently. If you want to use other Plugins you need 32-bit Plugins and 32-bit Firefox.