Palemoon supports add-ons and some older one. Cyberfox/Waterfox support newer add-ons.
From they way I understand it, Please correct me if I am wrong
Palemoon is a fork for Firefox
Cyberfox and Waterfox is rebuild of Firefox.
I find it odd that Waterfox, Cyberfox and Palemoon have 64 bit release versions when Firefox didn't have 64 bit aurora version now called Developer Edition. All Firefox had before was a 64 bit Nightly version of Firefox.