Well, that's kind of their whole point-- can AI be done in a way that guards privacy. It's not impossible even with cloud processing.
And "Trust" should be a big deal-- unfortunately most people don't care and Chrome has a much bigger marketing budget (and monopoly on Android).
Confidential compute (intel, amd and nvidia) already is a thing and has nothing to do with mozilla. Without such drastic measures, no, it IS impossible with regular cloud processing.