@ekaitz_zarraga @aral yeah, I noticed when I read the LibreWolf website after posting that. :\
Realistically for a fork to succeed long term it has to be taken under the auspices of a larger organisation, which I think Aral also mentioned.
If you fail to do that, then maintaining contributor interest becomes a struggle and external events outside of your control can kill the fork off prematurely.
Perhaps GNOME Web might be the dark horse solution? Most obvious issue atm is that it hasn't been ported to Windows or macOS.