Firefox 52 was the last release to ship with full-fledged support for XP and Vista. Since March 2017, users of these operating systems are able to only use Firefox ESR (Extended Support Release). As a part of the ESR, they only receive security updates which they’ll continue to get until June 2018.
Mozilla says that Firefox is one of the few web browsers that still supports Windows XP and Vista. With the release of Chrome 50, Google dropped support for XP and Vista, OS X 10.6, OS X 10.7, and OS X 10.8.
Notably, Microsoft pulled Windows XP’s plug in 2009, and the extended support was terminated in 2014. Similarly, Windows Vista also went out of the extended support cycle in April 2017.
Even in 2017, I still see some people using Windows XP. Currently, around 4.19% of all Windows devices run Windows XP, according to StatCounter’s September figures. The market share for Windows Vista is 0.79%. So, there won’t be many people who’ll miss Firefox on their computer.
Users running XP and Vista might want to upgrade their operating system or switch to some other browser. Running older versions of web browsers and other software exposes their system to newly discovered security threats.