If you don't (regularly!) donate to Mozilla to support the development of Firefox you have zero right to complain about them adding AI and other stuff.
How in the the hell are they supposed to fund their operation? Developing a browser is not cheap. They _have_ to try dumb shit like VPNs and AI and whatnot just to survive!
If you want that to stop then give them an alternative by donating: https://foundation.mozilla.org/en/donate/