https://digdeeper.club/articles/browsers.xhtml has a somewhat comprehensive analysis of a dozen of the browsers you might consider, illuminating depressing (and sometimes surprising) privacy problems with literally all of them.
In the end it absurdly recommends something which forked from Firefox a very long time ago, which is obviously not a reasonable choice from a security standpoint. I don't have a good recommendation, but I definitely don't agree with that article's conclusion: privacy features are pointless if your browser is trivially vulnerable to exploits for a plethora of old bugs, which will inevitably be the case for a volunteer-run project that diverged from Firefox a long time ago and thus cannot benefit from Mozilla's security fixes in each new release.
However, despite its ridiculous conclusion, that page's analysis could still be helpful when you're deciding which of the terrible options to pick.
So I haven't been following the Firefox thing that closely. Fennec isn't an alternative because it uses Firefox's Sync and Brave is out of the question because it's crypto Chrome?
Yes, I learned that thanks to DivestOS which was comming with Mull, they had a comparison table and yes no FF based browser support that basic security feature yet...
I use a similar set up. Librewolf on Linux and IronFox on Android. You could still use a Firefox account to sync, but I wouldn’t. I’ve heard there’s a way to host an older version of Firefox sync locally, but I haven’t looked into it.
Yes IronFox is a fork of Mull, and though it does have a couple of differences in opinion on the balance of privacy and usability, it's very similar. I've been using it since shortly after we lost Mull.
And this is the latest sync server that doesn't rely on discontinued versions of Python: https://github.com/mozilla-services/syncstorage-rs/. It's not a full, plug and play solution, and it doesn't support PostgreSql so I haven't set it up in my self hosted environment yet, but plan to eventually.
LibreWolf is what I use, but I heard Zen Browser is another fork that's been getting some traction. I don't use it though, but I've heard from someone who does that it works for them. thumbs-up