People read the headline and get angry, then want to tell everyone how angry they are. It's a badge of honour - look guys, I'm also angry.
Reading into their AI plans - it's to be run completely locally using only the data you want to give it, and it doesn't send info back to Mozilla.
Now, personally, my biggest issues with AI is data collection and where the training data comes from. It seems for FF, neither of these will be problematic, so I don't see the issue.