Pale Moon: End of Support for Windows XP

[Corrine]

As an advance announcement for the near future, Pale Moon will no longer be built for Windows XP from version 25 onwards.

Since Windows XP has reached its End of Life last April, and development of the browser has to move forward, XP support will be dropped in the next major version update. Although Windows XP is still used on many systems, continuing to cater to it means back-end development has to be held back in some respects, and preventing people on current operating systems from getting the full benefit of the available build options.

More at the source, including previous announcement about timeline for supporting Windows XP:  End of XP support in Pale Moon.