nightly updates for mac are currently disabled

[Kim Moir]

We were alerted to a problem with nightly updates to the macosx cross
compiled builds on Friday afternoon and updates were disabled that
evening. Essentially the app is not signed after an update is applied. If
you download the dmg it is signed, the issue only arises after an update is
applied.

Any builds downloaded as a dmg are signed as expected
https://www.mozilla.org/en-US/firefox/channel/desktop/

This is as result of the switch to taskcluster nightly builds last week.
This issue does not impact taskcluster opt and debug builds on trunk.

We are investigating a possible solution

Nightly on macOS loses code signature after update
https://bugzilla.mozilla.org/show_bug.cgi?id=1375904

Kim Moir
Mozilla Release Engineering