Librewolf is not primarily intended as the definite browser but a sane base template for easily customizable and extendable firefox builds.
The librewolf AUR package is a great starting point to make custom builds of firefox; between two json files in the settings repo you can tweak basically any relevant setting, bundle extensions (e.g. use custom forked ones without needing to either sign through Mozilla or disable security), search engines, use your own fxa/syncserver, handlers, branding, etc.
All in a git repo and you won't have to redo things next time you reinstall the browser or get a new machine (anyone else ever scratched their heads trying to recall that one about:config setting?)
Building and tweaking vanilla firefox yourself is quite an exercise. Librewolf makes it a breeze. The sane privacy-by-default standards is just the cherry on the top.
> use your own fxa/syncserver
Huh, is this tractable?
> Huh, is this tractable?
My opinion is "yes" - the source is available and runs as a docker container, the client setup is pretty trivial (on Android you'll need Fennec or another alternate build of Firefox to get at the settings). I'm aware of one user group running a shared instance and it seems to work as advertised.