Rated 5 out of 5 stars

Great Add-on. I am using it with growlnotify on a Mac as well (command: "/path/to/shellscript/growlNotify.sh" %subject %sender). As variables containing German special characters (äöü etc.) did not show in the growl alert, in the shell script I added a conversion from iso-8859-15 (my thunderbird setting) to utf-8:

BOF code:
#!/bin/sh
# thunderbird_wrapper.sh
# v1.0
# David LaPorte
# 09/23/05

#SUBJECT="$1"
#SENDER="$2"

SUBJECT=$(echo $1 | iconv -f iso-8859-15 -t utf-8)
SENDER=$(echo $2 | iconv -f iso-8859-15 -t utf-8)

APP="Thunderbird"
# Location of growlnotify (located in Growl distribution)
# You will need to move it from the DMG to a local path
GROWLNOTIFY=/usr/local/bin/growlnotify
$GROWLNOTIFY -p High -a "$APP" -t "$SUBJECT" -m "From: $SENDER"

EOF code
(save as UFT-8 file and make executable)

Hope this is useful.

Suggestion: It would be great to add a feature that the mailbox alert stays on the screen permanently after a certain period of inactivity (30s for instance) just like in growl.

This review is for a previous version of the add-on (0.16.1).