Not saying it cannot happen, but in Firefox, it is a “Recommended“ extension which gets reviewed per release. A sophisticated attack could slip through, but a ham fisted takeover is unlikely.
It's also worth mentioning that Firefox doesn't force you to auto-update add-ons, but Chrome/Chromium do. (There was a hack workaround to keep Chromium from updating, but I forgot what it was or if it still works. It wasn't a trivial option in the browser itself like it should be.)
It's also worth mentioning that Firefox doesn't force you to auto-update add-ons, but Chrome/Chromium do. (There was a hack workaround to keep Chromium from updating, but I forgot what it was or if it still works. It wasn't a trivial option in the browser itself like it should be.)