Rated 3 out of 5 stars

Another workaround for new versions.

0. Close Thunderbird
1. Log into https://console.developers.google.com
2. Press "Create Project", then "Create", and wait a minute until it's finished.
3. Click "APIS & auth", "APIs"
4. Find and enable "Calendar API" and "Tasks API"
5. Fill required fields in "Consent screen"
6. Open "Credentials", "Oauth", "Create new Client ID"
7. Choose "Installed application", then "Create Client ID".
8. Copy "CLIENT ID" and "CLIENT SECRET" values (will need them later)
9. Search on your hard disk for file with name "gdataSession.jsm" and open it
10. At the end of the file, remove everything after "Before you spend time trying to find out what this means, please note"
11. Append to the file this:

this.OAUTH_BASE_URI = "https://accounts.google.com/o/";
this.OAUTH_CLIENT_ID = "PUT YOUR CLIENT ID HERE";
this.OAUTH_CLIENT_SECRET = "PUT YOUR CLIENT SECRET HERE";
this.OAUTH_SCOPE = "https://www.googleapis.com/auth/calendar https://www.googleapis.com/auth/tasks";

12. Start Thunderbird and see if calendars work.
13. If not, try to add a new google calendar as usually ("new calendar"->"network"->"google calendar"). The app should ask you for your google login and password. Agree to everything ;)
14. You may need to re-enable all google calendars (just double click on them and click "Turn on this calendar".

Enjoy!

Đánh giá này là cho một phiên bản trước của tiện ích (1.0.2). 

Again, this is likely against some terms of service so I will not support this. If you want to go down this route I'd suggest trying the original provider again in a month or so.