I see what you mean. My first post of a link from this app and I guess I wasn't sure how this was going to look. I didn't want to post anything myself hoping the article would be self explanatory.
The question remains, is Firefox damaging my phone in the long run? Is fennec better?
No, I don't recommend Fennec. Consider Mull if you want something without Mozilla's telemetry. Mull has some of Tor Browser's privacy features as well as not having telemetry.
That said, I don't think Firefox is harmful in any way.
Honestly, I wouldn't worry about this. Chances are you'll replace your phone way sooner than any of this will come back to bite you. If it was bad enough to be a real problem, there would be much bigger sources talking about it.
I mean, I think the point is to know whether it's the loudest users or the majority of users.
I do think there's a serious problem of removing the human element though. Ticking off 20% of your users might not be a big problem ... unless those 20% of your users are your biggest advocates. That's where I think Mozilla at times loses the forest for the trees.
I love how people treat Mozilla and Firefox as the sole savior of browser space from Google despite being in bed with Google, while for Firefox to not be spyware (dials home on startup, DoH to cloudflare, glean, opt-out telemetry you can't easily disable, etc) and adware (pocket, "top sites", extension ads) laden garbage, people use forks like Librewolf, ignoring browser projects that actually respect your privacy like qtweb{kit,engine} browsers (falkon, qutebrowser), gtkwebkit browsers (badwolf, luakit), and SerenityOS's ladybird browser.
Hey, i hate Google as much as the next guy, but cut Firefox some slack man. It's the best compromise we could hope for, at least compared to the browsers you suggested with their abysmal UI & UX. The goal is for privacy to become mainstream, and no one without a bondage kink would ever touch theses with a 10 foot pole.
Okay, putting Google as default browser gives it undeserved trust from your everyday user who won't bother to change it : that's a big problem, but if you want it to change, consider donating ! This will help Mozilla free itself from the mega corps.
Honestly, love Librewolf but I was totally unaware of the other engines this mentioned. Are they as full featured? Do they have mobile versions to sync with?