https://www.theregister.co.uk/2017/10/05/mozilla_extends_and_ends_firefox_support_for_windows_xp_and_vista/

Mozilla has announced it will end support for its Firefox browser on Windows XP and Windows Vista.

The organisation offers Firefox Extended Support Releases (ESRs) that keep getting bug fixes for 54 weeks, even though nine new versions of Firefox should come along during that time. Mozilla offers ESR releases so that organisations with standard desktop environments can pick a version of Firefox and run it for a year, without the need to update their gold images.