I loved this addon... until it stopped working. Since a few months ago it simply does not show anything. It does not have anything to do with some incompatibility with other addons, disabling all of them but this, and with the Thunderbird default theme, it does not work. I guess it might have something to do with the new versions of Thunderbird, but I don't see anybody else complaining here. Very strange, but the fact is that for me it's like if I didn't have it installed.
EDITED: I love it again... I found out that it didn't work because somehow the Global search and indexer had been disabled. Fixed.