Review for Provider for Google Calendar by Radar Hill Web Design
Rated 5 out of 5 stars
Got the same issue as dryang where upon launching Thunderbird a window constantly pops up asking for Google credentials. Going into Preferences > Privacy and turning on cookie tracking solved the issue. Solid plugin with good customization options.
This review is for a previous version of the add-on (0.32).You can enable cookies in the Thunderbird preferences dialog under security.
To create your own collections, you must have a Mozilla Add-ons account.