Prior to this change the code that automatically updates prefs when an add-on is disabled, reenabled or uninstalled
could overwrite changes to a pref that were made manually by a user, either via the UI or via about:config.
This change introduces a check into each of those actions that verifies that the current state of the pref
is what we expect it to be based on the data we have about add-on settings, and if it is not then we
do not change the pref.
MozReview-Commit-ID: 5DpEg2fGwIW
