Yep, tried again and it happens only if interacting first with Firefox in the .dmg image. Seems to be happening with older ones as well (90.0a1) and with other random app as well (disk maker X .dmg).
Bug 1729306 Comment 2 Edit History
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Yep, tried again and it happens only if interacting first with Firefox in the .dmg image. Seems to be happening with older ones as well (90.0a1) and with other random app as well (disk maker X .dmg). Still on macOS 11.5.