Rated 5 out of 5 stars
Brilliant! This solves a long standing shortcoming in Thunderbird. Many thanks to the author.
It works fine with Thunderbird 6. Until the author makes an update you can tweek it yourself. Open the xpi file with an archive program like 7zip, extract install.rdf and edit the file to change maxVersion to 6.0, then update the xpi archive and proceed with installing the add-on.