Rated 5 out of 5 stars

Does what it is supposed to: Enablement of the google calendar tab extension on Thunderbird 60!

Some remarks though:
- The "Open Google calendar in a Thunderbird tab" icon is a wee bit big and makes the toolbar unnecessarily bigger in height
- Support for Thunderbird beta (currently 64.*) would be great (however, I guess this extension would have to be converted to the newer webextension format)...