You are aware translation services are available that are neither a local LLM nor Google-owned, yes? We had machine translation before ChatGPT existed, and I don't think that tech evaporated in a sudden fire just because a more harmful option appeared.
The appropriate option for Mozilla would've been to not include AI at all. If they really, really couldn't have swung that (they could've), then the second best option would be having all AI features set to off-by-default. Instead, we've got on-by-default. That is unambiguously a terrible idea.