Rated 5 out of 5 stars
This addon was great while it worked.
It stopped working after thunderbird version 60.
Today thunderbird 60.xx was no longer launching so i had to update to the latest version (i am using a rolling distro and was keeping thunderbird from updating so it would still work with this addon).
However the new thunderbird versions brought back compatibility with alltray.
Now it works to simply add "alltray -H thunderbird" as a command to be executed as a startup application. You will need to install alltray by following the specific steps for your distro.