The theme works in Firefox, Thunderbird and Sunbird. (See also: http://gulp21.bplaced.net/addons/history.html)
Version 2.4 works only in Firefox 3.6 and Thunderbird 3.1.
Version 2.3 works only in Firefox 3.5 and Thunderbird 3.
You can download version 1, which works in Thunderbird 2, Sunbird and Firefox 2, after clicking on "View Older Versions".
More informations, screenshots and pre-versions can be found here: http://gulp21.bplaced.net/addons/own/en/index.html.
If you want to change the look of own, you can use the extension Gulp21 Theme Modifier: https://addons.mozilla.org/en-US/firefox/addon/7514
If you don't like the new Forward-/Back-Buttons, you can use NoUn Buttons: https://addons.mozilla.org/firefox/addon/7056
If you like this theme, please write a review or criticize something.
Use http://gulp21.bplaced.net/addons/support.html for reporting bugs.
A buglist is here: