@rauschma Unlike computers, phone operating systems compete on services they offer, for example iCloud on iOS; not on the OS itself which is essentially trivial and only for supporting the services.
Mozilla has none of these services.
This is why Microsoft failed as well, arguably even having some of the services and plenty of resources.
@thomasfuchs Mozilla providing those services (e.g. everything that Proton provides) could be a good fit and make them money.