Devices
New phones appear here as pending. Approve one to a user to let it browse; revoke to lock it and wipe its stored logins.
Users & logins
Extensions pushed to devices
These install automatically and can't be removed by users. Paste the Firefox add-on install link (on the add-on's Firefox Android page, the "Add to Firefox" / latest.xpi URL). Scope to everyone or one user. The per-user switch (on the Users tab) decides whether that user may also add their own.
App updates
Upload a signed APK, then activate it. Approved phones will be offered the update. Mark it mandatory to require it.