Developing a community based browser engine that remains up to date with all the updates to the html, css, and javascript standards would require an immense amount of infrastructure and monetary backing. Essentially Firefox's Spidermonkey is the closest we have.

I'd be curious if Mozilla could somehow get enough funding without Google or Microsoft or any other big tech corporate funding/influence and still keep up to date with new features and security patches. Doesn't seem likely though.

Librewolf on Linux Desktop with NoScript, Chameleon, etc. Mull on Android mobile with similar. (Both are firefox based).

I'm on Graphene OS for mobile though, which necessitates the use of Google's Pixel and uses a hardened Chromium based browser called Vanadium. Main dev has criticized Firefox for being insecure in the past, but still use Mull anyway...