I mean, it sounds like it's basically just a fork of an old version of Gecko/SpiderMonkey, because it looks like it definitely doesn't have the same latest stan

I mean, it sounds like it's basically just a fork of an old version of Gecko/SpiderMonkey, because it looks like it definitely doesn't have the same latest standards support that current versions of Firefox have (based on the Pale Moon website). Which, as an aside, I think is hilarious, because they claim standards compliance as one of their biggest features.