But if we’re talking about ideals, then why wouldn’t you advocate for change towards great design versus stagnation? Now if you don’t trust Mozilla to pull it off, then that’s a different argument than so far has been made.

While I don’t personally know the designers at Mozilla, I’m doubtful that they simply “wanted to be cool like Google” and instead did their own research. I could be wrong but usually work isn’t so arbitrarily done for large products and teams.