Waterfox for the most minimal touch, it's just FF with no Moz Corp in it and no other changes.

Librewolf for very hardened privacy defaults, even the sort of setting that sacrifices ease of use or compatibility in favor of privacy.

uBO works on any FF fork, i believe it's included by default in Librewolf. Waterfox has a native adblocker but it disables itself if you use uBO.