In October 2017, Mozilla announced an end of life date for Firefox on Windows XP of June 2018.
Firefox users on Windows XP got automatically upgraded to the extended support release (ESR) version. This is a slower-moving branch of Firefox that waits longer to add new features than the normal branch.
Thus, Firefox 52.9.1 esr is the final edition of Firefox to hit Windows XP. It won’t see any future updates, including security patches.
Mozilla Firefox 52.9.1
