I know the other thread got locked, but since several people had mentioned Pale Moon and Basilisk in the discussion, I just wanted to take the occasion to say that the Red Cats Green and Blue full themes work fine in both browsers.
For Basilisk, you can use v.6.1.0; for Pale Moon, you need v.6.0.0 (v.6.1.0 won't work).
To the best of my knowledge, Moonchild Productions, the producers of Pale Moon and Basilisk, have no intention of deprecating the use of full themes on either product.
I have not written this in the sense of "browser evangelism"; as an old friend frequently said, "Ya pays ya money, ya takes ya choice".
A healthy and peaceful 2019 to all.
