Update 3.1 Rated 5 out of 5 stars

@David. Sure you can think of viruses. But I'm not going to upload it to Mozilla because I've validated it up to version 3,5

How to do it yourself:
Via 7Zip open the XPI. Select the file install.rdf and edit these lines:
3.5
2.1.682b

Close your text editor and 7Zip will ask to update the package. Now you can install the XPI in thunderbird.

I've added on the version a 'b' to see the difference with the original one.

This review is for a previous version of the add-on (2.1.682).