Firefox will work in Windows XP, but doesn't work in windows with Service Pack 1 and 2(Service Pack i'm not 100% sure), but in Service Pack 3

'''Debapriyo Bhattacharya''' if you read my post after the post you copy+pasted from in https://support.mozilla.org/en-US/questions/987005 you would have seen that the minimum for Firefox on Windows in WinXP '''SP2''' and not SP3 ever since Firefox 13.0 release. Diego Victor even said he was unsure. http://www.mozilla.org/en-US/firefox/27.0.1/system-requirements/ http://www.mozilla.org/en-US/firefox/13.0/system-requirements/ I have not seen any plans for WinXP SP2/SP3 to be dropped anytime in near future still. You will still be able to keep up to date with Firefox however your WIndows XP itself may potentially get more vulnerable over time.