As a long time computer profeesional, I have to say, all this FUD ab out WinXP is way overblown. As an experiment, I have a WinXP machine that hasn't had an update since 2007. Never a virus, never a problem. Keep the version of Firefox that works and leave it alone. Run current AV/anti-malware and you'll be fine. XP has a couple more years of useful life.
And Windows 8 is worse than Millennium Edition was! What a piece of crap! But we've been lulled into thinking Windows or OSX are the only games in town.
Personally,I have only one Win & machine left, all the others now run Linux Mint. Definitely more intuitive than Win 8!