Firefox supports Windows XP and Vista until september 2017
Firefox will the operating systems Windows XP and Vista from september 2017, not more support.
That makes browsermaker Mozilla on his own website known. The group of users that have Firefox use on these obsolete systems will be from march 2017 and also less recent updates. From september 2017, there will be no security updates anymore.
This does not mean, however, that the browser no longer works on Windows XP or Vista. But because of the lack of updates there will be after september 2017, vulnerabilities arise that are no longer to be bridged by the company.