

There are others, such as Mercury and Floorp, but I use Librewolf. I think it’s great!
It depends on your priorities. Librewolf is basically just Firefox, but with some enhanced privacy features, while Zen is like a whole different browser. I can’t say what you would prefer.
Edit: Mercury is no longer developed, it seems.
Well, I do believe basically every fork is basically the same as far as that goes, except for Zen, which is a little more opinionated in terms of personalization. However, if they’re Firefox forks, you can enable
user.js
hardening anduserChrome.css
personalization.Librewolf is faster than regular Firefox, in my experience.