Just stumbled upon this project, seems rather new as my DNS blocked its domain by default for being too new hehe.. Anyone had a chance to try it yet? Its got some hefty promises, like having equally strong privacy features as Librewolf. I'll be giving it ago at least, almost sounds a bit too good to be true...
Until something comes out saying otherwise, Mullvad browser seems to be the best privacy wise.
I believe Zen is better than default Firefox out of the box, but you can get the same effect in regular Firefox by toggling some options.
I liked Zen for the UI changes. It's nice having the tabs on the side and a customizable sidebar