The setting exists, but may or may not actually be respected based on user reports.

Just like their auto-updates, you can turn the option off, but whether the feature is actually disabled is another question entirely.

I don't trust Mozilla enough. For one, not giving UI options and hiding all the settings in about:config where non-technical users can't access is a shitty thing to do. Second, I have zero trust that the settings actually do anything since many don't.

I don't believe for one moment that turning off their AI features actually 100% prevents that code from running.

You can turn the existing AI off if you learn the magic incantation for about:config, its not very usable. I would hope they will provide some proper switches in the settings menu for each of the AI features they intend, including the one for automatic tab grouping (which so far is total garbage and a complete waste of CPU).

They’ll let you turn it off until people don’t care as much, then it will quietly become mandatory. Only some of the nerds will even care, since by then the panopticon will probably be fully constructed.