It does not show up in the UI once disabled, does not re-enable again and does not pester the user into enabling it again as proprietary software often does.

I can understand criticism on the development time that may have been better spent, but less criticism against the existence of something that is fairly easily disabled and not user-hostile in intent.

I disabled the AI stuff immediately on my side (through the regular UI, not about:config settings) and never saw anything AI-related in Firefox afterwards.

It's worrying seeing Firefox getting so much more criticism than all the more user-hostile browsers that end up benefiting from such somewhat unwarranted criticism against the most popular non-hostile browser.