The useragent of all firefox mobile users is the same. A couple of different devices all got the useragent: Mozilla/5.0 (Android; Linux armv7l; rv:2.1) Gecko/20110318 Firefox/4.0b13pre Fennec/4.0 The problem is that there is no device information in the UA so from the UA it's not possible to know what device is browsing your website. The WURFL project: http://wurfl.sourceforge.net/ is based on UA so mobile devices get other stylesheets on pages than desktop browsers. Without device information and android version in the UA firefox mobile is not easy to use.