Depends on your specific case, but IMO in order of preference for deskop, Tor Browser as much as possible, followed by Mullvad Browser as much as you can, for scenarios where you cannot use Tor Browser, followed by LibreWolf for the few sites that require persistent logins (you'll need to enable setting cookies for those specific sites). There's also other Firefox forks like GNU IceCat (unofficial binary for it), Floorp and Zen Browser.

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.