I was wrong on WebExtensions

WebExtensions > legacy addons.
Firefox legacy addons basically have unrestricted, full access to everything browser does.
They are barely step behind ActiveX. They can download arbitrary data and execute it.

Basically what i'm telling you:
Legacy Addons==Do w/e you want, Run random executables from internet.
Firefox was right on deprecating them and WebExtension permission model is superior to blanket consent to do anything.
WebExtensions==permissions, restricted, sandboxed.

https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/permissions