Assuming you are running 4.0, it's the second-from-right tab in Options (image attached)

'''<u>Your User-agent</u>''' indicates that you are using Firefox version 3.0.3 and some other possible problems and causes for an incorrect version: *Your User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; '''''rv:1.9.2.12''''') Gecko/20101026 '''''Firefox/3.0.3''''', '''''Ant.com Toolbar 1.3''''' ( .NET CLR 3.5.30729) **'''''Firefox/3.0.3''''' indicates Firefox 3.0.3 **'''''rv:1.9.2.12''''' indicates Firefox 3.6.12 (if I am not mistaken) **'''''Ant.com Toolbar 1.3''''' indicates that you have this toolbar installed and it could be causing your problems #Uninstall the Ant Toolbar #*See: http://forums.mozillazine.org/viewtopic.php?f=48&t=1378465 (''appears this is still a problem 18 months later'') #*See: http://support.mozilla.com/en-US/kb/Uninstalling+add-ons #*See: http://support.mozilla.com/en-US/kb/Cannot%20uninstall%20an%20add-on #Reset your User-agent #*See: https://support.mozilla.com/en-US/kb/Websites%20or%20add-ons%20incorrectly%20report%20incompatible%20browser (''reset ALL user-agent prefs'') #After doing the above, exit Firefox, then start Firefox again. '''<u>Sync</u>''' was not automatically included as part of Firefox until Firefox 4. If you are using a version prior to Firefox 4, you can install Sync: *Download/install link: https://addons.mozilla.org/en-US/firefox/addon/firefox-sync/ *Info about Sync: **https://www.mozilla.com/en-US/mobile/sync/ **https://support.mozilla.com/en-US/kb/what-firefox-sync