On Firefox OS (FxOS), every app has its own set of permissions. The OS makes sure that an app may only do things that are requested in the app manifest. Some of these permissions are always set to Ask. This gets exceedingly difficult to explain to users. To bridge this gap, I have created a developer settings that shows a verbose app permissions list. This feature only targets the Privileged apps that come through the Marketplace. For now, we can not revoke permissions for the built-in apps (the permission set() call throws)”]
Source: https://frederik-braun.com/revoking-permissions-on-firefox-os.html