Review for Provider for Google Calendar by musbenziane
Rated 2 out of 5 stars
Seems useful, but very unreliable.
Changes on google calendar side causes it to go into a loop, either force the local changes back into google calendar, or you stay in the infinite loop (you click discard, and it keeps popping up making thunderbird unusable).
To create your own collections, you must have a Mozilla Add-ons account.