Or just patch the binary to remove the check, like what real users did when they encountered software they didn't like 100% the behaviour of, whether or not they had the source.
(Yes, I know Firefox is open-source and you can theoretically compile it with the check removed, but that is going to take far more time and effort than finding and NOP'ing a jump.)
Yeah that one! I wonder when the first installer comes around patching known versions of Firefox to accept unsigned addons to dump their awesome toolbar onto the user. (Or just outright overwrite the users Firefox with an own version of Firefox, not including said check)
(Yes, I know Firefox is open-source and you can theoretically compile it with the check removed, but that is going to take far more time and effort than finding and NOP'ing a jump.)