Developer reply by Tomasz Lewoc
Rated 4 out of 5 stars
Since the Last two updates from Thunderbird the Add-On did not sync any more.
It would be great when the developer can fix that bug!
Thanks Rainer
I just tried on 45.5 on Windows and Linux and it worked in both cases. Try creating a new Thunderbird profile and installing the add-on there.
To create your own collections, you must have a Mozilla Add-ons account.