TBA: Set new preferences after update
The current implementation of distribution preferences is intended for use only during the initial installation/initialization. Specifically, it should only be set soon-after a new gecko profile is created.
We're currently abusing this feature, and trying to set new preferences after we install a new version of the app (updating). Unfortunately, this overwrites any user-modified preferences, too. We should extend the current implementation so it does what we want but it shouldn't make surprising changes when the app restarts or updates (such as reverting user-modified prefs).
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information