I think I disabled "Use AI to suggest tab group names" and "enable link previews" in settings (not about:config), and I don't really see any AI anywhere else? I can add/remove some chat thing from the sidebar, but you can just remove that button and you don't need to use it. It's like any other feature one may choose to not use.

I now see there's also a "Create alt texts automatically" for pdfjs. This actually seems one of the more useful AI features I've seen. But I've never noticed it exists as I don't need this accessibility feature. You can disable it in the pdfjs (no about:config needed).

In short, Firefox is not forcing anyone to use AI and ways to disable it are not that obfuscated.