Comment 17 for bug 709125

Well, it's still possible to differentiate an Ubuntu machine from Mac OS X and Windows, it just isn't possible to differentiate it from another Linux machine.

In any case, this isn't going to be changed in Firefox (https://bugzilla.mozilla.org/show_bug.cgi?id=572650 details the reasoning behind this, and this isn't something we are going to support indefinitely as a distro-patch, and I can't see Mozilla ever agreeing to us reverting this change either). In addition to this, as I pointed out above, having "Ubuntu" in the UA string has been a long-standing source of problems such as this: http://askubuntu.com/questions/16014/web-sites-see-my-firefox-as-a-mobile-browser-on-ubuntu (and plenty of bugs reported on Launchpad too).