There are many features you are not using in all your software. Just being there, should not be a problem for people. You should evaluate a software by what it's giving you, and which harm it brings, not by what it's giving others you do not care about.

And so far, we can assume that AI in Firefox will be like all the other stuff people don't care about, just optional, a button here, a menu-entry there, just waiting for interaction, but not harmful.