Thunderbird 3.1.2 Rated 5 out of 5 stars

It is easy to correct: unzip the file .xpi (maybe modify the extension from xpi to zip) , open the file install.rdf and change the line
zip the archive, change the extensio from zip to xpi and install it.

This review is for a previous version of the add-on (1.2).  This user has a previous review of this add-on.