I’ve tried all the Firefox forks I could find, including LibreWolf. It’s not your no-brainer “Non-Mozilla Firefox” you can just switch to.
Basic browsing may work, but nothing remotely close to “web-app” will, because they disabled all modern APIs due to privacy concerns.
I'm currently using Iceraven on my Android phone and it's mostly a great experience! It gives access to all sorts of add-ons to block ads, cookies and other internet annoyances, some of which are not yet available on the official FF Android app since Fennec was abandoned.
Even if speed were not 100% that of certain mobile browsers (I have not benchmarked them nor noticed any major differences), having no banners show up make up for it. I have no concerns with telemetry, but the Iceraven folks have cut down on some of the telemetry.
In fact I use Iceraven as my default YouTube mobile app, instead of the official app. With the right add-ons, it makes for a quite nice YT experience!