Imagine how useful in securing users from malicious addons and all unwanted data collection this would be — you could block every single addon which has no online functionality. I would assume that the vast majority run their core functionality locally.
And we should be able to blacklist/whitelist sites for each add-on, and specify an order of execution for add-ons (for each request, this add-on goes first, then this one, then that one, …).
Request it: https://bugzilla.mozilla.org/enter_bug.cgi