From his lack of response on the topic it’s clear he still supports that position (being anti-gay marriage). He was ousted in part because Mozilla is supposed to be and open and inclusive place to work, hard to do that when your boss doesn’t believe you should be allowed to marry.
Furthermore he proved his lack of morals and character by starting a crypto browser. This guy isn’t worth defending.
Jobs fire people ALL THE TIME over personally held beliefs or things they say/do outside of work. We can argue that’s not right but as long as it happens to the rank and file I think it appropriate to at least try to hold C-level to the same standards. If it helps you sleep at night I’m almost sure he would have survived the backlash at any company that wasn’t like Mozilla, lord knows C-level came get away with murder most places.