Rated 5 out of 5 stars

Works for me with Thunderbird 3.0.4 and Lightning 1.0b1 in Linux. At first it installed but would not export file upon exit. Repeated - still would not work. Unzipped the .xpi file, opened install.rdf with text editor, changed em:maxVersion to ="9.0pre" in both locations. Zipped up the open files(but not the folder they were unzipped into) and renamed that to the original .xpi file name. Reinstalled and it works.
Seems to work very well based on a couple of trials.

This review is for a previous version of the add-on (0.3.2). 

can youe explain the reason for the maxVersion?
it sounds like ...
with this fix you are able to export on close.