Firefox version 52.9.0 ESR is famously the of the browser to support legacy operating systems like Windows XP and Windows Vista . Released in June 2018, it marked the end of an era, serving as a "lifeboat" for users and businesses who couldn't—or wouldn't—upgrade their hardware or OS. The Role of the "Extended Support Release" (ESR)

If you understand the risks and have a controlled environment, the official Mozilla archive provides a clean, unmodified copy of – the final guardian of the old Firefox world.

A fork of Pale Moon that continues to support XP with modern web compatibility improvements.