https://mail.mozilla.org/pipermail/tb-planning/2018-May/0060... says "Manual updates of 60.0 will be the initial update mode, as we often
do for a new release, because of the breadth of fixes and improvements. Manual-only updates (and updates via downloads) allows us to do a slow
rollout to users, to get more user feedback than is possible during the beta period. Automatic updates will be enabled when we are satisfied
that we have sufficient numbers of users and a sufficient level of quality - a process that typically takes some weeks."