Revert "Bug 930104 - Remove localId=0 hack for the system app on firefox and correctly set permission for any app loaded in Firefox r=vingtetun"

This reverts commit 09eb15afda938974376c6e33117ac84c98353bf0.
Merge pull request #13819 from KevinGrandon/revert_bug_930104

Revert "Bug 930104 - Remove localId=0 hack for the system app on firefox and correctly set permission for any app loaded in Firefox r=vingtetun"