here's a tl;dr

1. can only disable non-"Mozilla approved" addons. uBlock Origin is approved.
2. it works not by remote trigger, but via a site blacklist (but that blacklist can probably be updated remotely). upon visiting a website that is in the blacklist, all "unapproved" extensions will be disabled
3. when extensions are disabled, you'll get a banner in the extensions overflow button in the toolbar, but you won't see the banner unless you click the button, and you won't have any banner if the extension is not in the overflow menu (for example, if it's pinned to the toolbar)
4. the feature can be disabled in about:config (at least for now) by setting extensions.quarantinedDomains.enabled to false
5. Mozilla's Bugzilla page for this feature was initially tagged for the group firefox-core-security but was quickly moved to mozilla-employee-confidential
6. Chrome has been doing this for a long time