Because Microsoft ended support for Windows XP in 2014 and Mozilla ended support for this version in 2018, using Firefox on XP today presents significant security risks. Final Version : Firefox 52.9.0 ESR.
: Only the 32-bit version is compatible with Windows XP; the 64-bit version of Firefox requires Windows 7 or later.
The latest and final version of that officially supports Windows XP (English) is Firefox 52.9.0 ESR (Extended Support Release), which was released on June 26, 2018.