One thing that seems to be common amongst many of these Firefox forks is they're very difficult to find which official version they're equivalent in functionality to. This one is no exception.

This is actually based on the Goanna web engine (a fork of the Firefox / Gecko web engine) derived from the https://www.basilisk-browser.org/ . You can find out more here - https://forum.palemoon.org/viewtopic.php?f=69&p=275829#p2758... .

Probably because there often isn't a straight answer to that. I've no idea about the progeny of this browser, but I've seen several Firefox forks "interbreed", borrowing patches and feature backports from each other. So there might be a specific version of Firefox you can ultimately trace the repo to, it likely has code from newer versions spliced in. At least, that was my impression.