eUXP is, as you guessed it, a fork of UXP.
Right now, only Basilisk (unofficially) and Dactyloidae use eUXP.
It's easy to swap your XUL app to use eUXP. Swap the platform URL in .gitmodules from UXP's to eUXP's. No extra modification needed.
Dactyloidae 13.2 nightly (Windows 64-bit)
Snake browser (GitHub Actions for eUXP) (Windows 32 and 64 bit)