Numerous web browsers have already stopped supporting Windows XP and Vista, but not Firefox. To this day, Mozilla's latest software can work with your decade-old PC. However, even that team has its limits -- it's phasing out support for XP and Vista starting next year. Mozilla will start by moving users on these operating systems to the Extended Support Release in March 2017, limiting them to feature updates that can be "several cycles" behind the curve. And while the company plans to unveil a final support end date in the middle of that year, it'll effectively cut the cord in September, when it stops delivering security updates.