If anything the non Developer Editions of Firefox disabling the ability to load an extension locally (without resetting it every time the browser starts) closes one path to preventing auto-updating of extensions.
That's a path necessary only in Chrome - Firefox allows you to disable auto-update of extensions, both wholesale and individually, without extraneous steps like that.
(The ability to load extensions locally would be great for its own reasons, but that's irrelevant to this discussion.)
There are very few users, so no one buys the extensions.