@Fabby "Feature Flagging with Normandy Pref Rollout
Normandy Pref Rollout is a feature that allows Mozilla to change the default value of a preference for a targeted set of users, **without deploying an update to Firefox**. This document focuses on the use of Pref Rollout as a mechanism to enable feature flagging in Firefox. " from https://wiki.mozilla.org/Firefox/Normandy/PreferenceRollout