The "update_url" is not used by Firefox in the root of a manifest; your add-on will be updated via the Add-ons site and not your "update_url". See: https://mzl.la/25zqk4O
Le "update_url" non es usate per Firefox in le radice de un manifesto; tu additivo sera actualisate via le sito Additivos e non via tu "update_url". Vider: https://mzl.la/25zqk4O