I am on the Release channel, and *Thunderbird* notified me of the update, which may be contrary to others who were updated through Kaspersky or other service. Now, in addition to losing my Gmail Provider calendars, TB periodically and repeatedly becomes unresponsive for up to 3 minutes before returning control. During this time the processing wheel is turning. This appears to be isolated to TB, as I can do anything else with any other program or the desktop during this period. The Task Manager reports no abnormal CPU /Memory activity or unexpected app activity. So far it is merely an interrupting annoyance that I would otherwise use to check email, .......