I'm all for somebody forking Firefox circa 3.6 and just backporting security fixes to it, but I suppose Pale Moon is as close as we'll get, which is fine.
You say a lot of things that sound like you're using them as insults, but I wouldn't really consider them so. That Mozilla has moved on from a good place in their development and now their new crazy schenanigans are no longer compatible with said "good place" is not really a criticism of a fork from that spot.
Heck, Moon Child has been breaking addon compatibility already, because the old UI code isn't compatible with updated addons.
This seems like rather a contortion to place the blame on PM. In fact, Firefox is breaking compatibility with older versions of itself, and PM is just trying to tag along for the ride, while not just being a reskinning, which is of course the problem--if PM was just a reskinning, all the extensions would work. But the interface got so fucked with Australis that the whole point of PM was to point at Australis and say "not that."
And there's always the archives of previous versions of extensions, although a lot of those will presumably stop working as FF and PM diverge, if they involve a server component.
I'm not saying PM is the best way to go about the FF situation, but at a certain point people just started saying, "Fuck it; I'm tired of FF's shit." Which is a bit sad really, as we want to use FF but they keep poking us in the eye.