If you try to repeat the process, the log in screen never pops again until you quit and restart Thunderbird.
The following is in the error console:
[calGoogleSessionManager] Reusing session tc...@ngs.org
----------
[calGoogleSession] Token expired 1421949032 seconds ago, resetting
----------
[calGoogleCalendar] Logging in session tc...@ngs.org
----------
[calGoogleCalendar] No access token for tc...@ngs.org, refreshing token
----------
[calGoogleSession] Adding item https://www.googleapis.com/tasks/v1/users/@me/lists to queue
----------
[calGoogleSession] Adding item https://www.googleapis.com/calendar/v3/users/me/calendarList to queue
----------
[calGoogleCalendar] Failed to acquire a new OAuth token for tc...@ngs.org data: { "error": "http_401" }
Thanks in advance for any assistance!
Cheers,
Tony