It's tricky to get the ux of this right. Say you don't want to give Firefox background access because it should only be active while you are actively browsing. Then that one time when you are about to download a 4GB iso, you start the download and minimize the app or even close the phone, when you get back the download was cancelled after just 2%. :(

Not saying it can't be done, just that there are many corner cases that can easily "break the internet" for non tech users if not handled in a smart way.