Rated 4 out of 5 stars
I love this extension, but there's a problem in Firefox 3.6.
Trackpackage 2.5 - and problem still exists in 2.6 - adds a huge mess of buttons in the toolbar config editor in Firefox 3.6.
Seems to be ok in Thunderbird, where I use it the most.
I've emailed the dev twice about it now, but still no resolution.
Will change to 5 stars once this is resolved.