Review for Provider for Google Calendar by peterbecich
Rated 4 out of 5 stars
This add-on was super useful to me but seems to be broken in Thunderbird 58. Many thanks for its past usefulness, though.
Edit: See these links for an alternative solution, using CalDAV.
https://blog.mozilla.org/calendar/2013/09/google-is-changing-the-location-url-of-their-caldav-calendars/
https://developers.google.com/google-apps/calendar/caldav/v2/guide#connecting_to_googles_caldav_server
To create your own collections, you must have a Mozilla Add-ons account.