Rated 4 out of 5 stars

ద్వారా Era పై అక్టో. 30, 2016 · పెర్మాలింక్

The button must be added manually: right click on the toolbar, Customise ..., Drag and drop the Thunderkeep button in the toolbar.

I updated the project and fixed the issue in this new addon
https://addons.thunderbird.net/thunderbird/addon/google-keep-tab