well, for one firefox is not a stripped down browser but one with conveniences like push notifications, safebrowsing and other things, while ungoogled chromium is a specialized browser built for those who don’t need all that. don’t forget also that chrome can’t be patched up on many fronts, ublock’s dev gorhill has written about them here

that being said, mozilla could make a first time setup page with an option for convenience and another with a menu for selecting which services do you want. but I wouldn’t hold my breath