They aren't taking away control. Read their own post
Give me full control of all features or I go elsewhere.
That's what's happening here. A feature for which the UX is still in development, and until then, interested users can manage it via the about:config page.
Should I read their own post again?
Why not ask user first? "Do you want to disable add-on not monitored by Mozilla on this specific site?".
Also, how many times users asks about this functionality? "I want Mozilla to monitor add-ons installed on my browser and disable it on some websites, when Mozilly want it" - surelly most of the users wants this.
https://bugzilla.mozilla.org/show_bug.cgi?id=1832791
Upd:
> We need to have ability to set the list of quarantined domains remotely.