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.