For a less complicated alternative, just swap out Firefox with LibreWolf. Just make sure to read the ENTIRE docs to save yourself from any nasty surprises. Especially about RFP (Resist Fingerprinting), WebGL, Canvas, etc.
On Andriod, again, there's Tor Browser, IronFox, Fennec F-Driod. Additionally if you want a browser based on a different engine, there's Cromite, which is based off of Chromium, but it's probably better to stay with a less commonly used engine like Firefox rather than keep using the mainstream monopoly of Google.
As an aside, this video helped me understand some stuff better and it seems to be less of Mozilla being untrustworthy and more about them being total losers in communication. I recommend checking it out.
Oh also, Ladybird Browser, is being developed. It is not based off of Mozilla Firefox or Google Chromium or Safari. They're building their own browser independently without getting any code from other browsers.
The Alpha release is planned to come out on 2026.
Impossible to take them seriously if they have already started off on the wrong foot using exclusively megacorpo proprietary platforms for coms. If your developer / testers privacy doesn’t matter since they opted for Microsoft GitHub & Discord, what would lead you to believe their project would take privacy seriously?
I somehow missed reading about the part about syncing. Pretty sure LibreWolf and IronFox does allow that as well, you need to enable it somewhere in the settings and log into your Mozilla account I guess.