Just a quick note that Mozilla is planning to phase out support for Windows XP and Windows Vista. Starting with the launch of Firefox 53 in March 2017, these two old operating systems from Microsoft will no longer receive feature updates from Mozilla. The browser developer explicitly mentions that it will block installs of Firefox 53 on XP and Vista.
At the moment, Mozilla is the only major web browser that still supports XP and Vista. Ghacks reports users of these two operating systems will be need to stick with Firefox 52, this version of Firefox will receive security updates until mid 2018.