Palemoon is actually not a fork of firefox, or technically it is, but it’s not based on any recent firefox code. Their engine is a fork of gecko that separated years ago and they are doing their own independent thing. Compatibility is not nearly as good as FF based browsers.
In the Same vane there is Basilisk, which was started by the palemoon team but is a separate project now with it’s own developer.
Garuda ships a fork of Floorp as their browser now (used to be based on librewolf but now floorp), which looks interesting as well, and more usable to me than Floorp itself, who’s website, last I checked, wasn’t even fully translated to english yet (it’s japanese), and there was very sparse info on what the point of the whole project was even supposed to be.