Developer reply by Günter Gersdorf
Rated 5 out of 5 stars
I really like the way it works and that it is highly customizable via userChrome.css.
But unfortunately it stopped working with TB20 (Earlybird). It now shows the size of the email instead of the name.
You can download a fixed version from http://www.ggbs.de/extensions/
To create your own collections, you must have a Mozilla Add-ons account.