Unofficial Google Keep add-on for Thunderbird, it adds a button that opens a Google Keep tab in Thunderbird. The home page of the extension contains some pictures and reviews.
Open Thunderbird, go to Tools -> Add-ons -> Extensions, search for Google Keep in the serach box and click on "+ Add to Thunderbird".
Download the repository, zip it, rename it to Google-Keep-Tab.xpi and choose install addon from file in Thunderbird.
In linux the xpi file can be created with the following commands
git clone https://github.com/Garoe/Thunderbird-Google-Keep-Tabcd ./Thunderbird-Google-Keep-TabVERSION=$(cat ./manifest.json | jq --raw-output '.version')zip -r "../Google-Keep-Tab-${VERSION}-tb.xpi" *