Automatic updates for Release channel are disabled the day after Release (Wed) and then enabled again on Friday if all is well. You can still manually check for updates.

See Releases Scheduling calendar

Are you saying if Firefox update is set on,

"Check for updates but let me choose whether to install them"

I should receive a notification on the day a new version is released.

What does the notification look like when a new version of Firefox becomes available?

hi jorb, in the first days after a release date, the automatic updates are usually gradually rolling out: at first the updates are only offered to a smaller percentage of users and then halted again in order to evaluate if there are any major issues with the new version (by looking at incoming crash data for example). if everything works well then auto-updates are fully unthrottled, otherwise they may stay turned off until a fixed version is being pushed out. currently for 47 we're in the unthrottled phase and updates should be reaching the whole firefox population. your installation will check for an available update every 8 hours. as far as i understand the process, you'll first receive periodic unobtrusive notifications that an update is available and after a certain time not acting on it a full dialog window will open informing you of the update with the options to perform it now or ask again later.