windowscentral[.]com/software-apps/an-absolute-legend-is-actively-developing-a-modern-web-browser-for-windows-xp-and-its-fantastic
github[.]com/Feodor2/Mypal68/releases/tag/68.14.4b
Dusted off my XP VM and it does work. It's a ZIP file with no installation -- just unzip & run.
It's based on Firefox 68, hence the number in the title. Way behind the version of Firefox you'd use now, but obviously there are limitations to what can be achieved on such an old OS. More specifically, it's based on the Pale Moon browser, which itself is a fork of Firefox code. It supports some extensions, has Brave as the default search engine, and from what I can see, is utterly brilliant.