Maybe I'm missing the point but the mozilla platform doesn't meet you're needs? I know it's not a pure python solution but there's work in progress to use python as a scripting language instead of javascript to develop the components. I did not made anything on the python + XUL side but tested 2 years ago in javascript and it was neat. The book Creating Applicatin with Mozilla was very helpfull (BTW, if I'm not wrong thunderbird and firefox are both build using the mozilla platform/XPCOM/XUL)
<br><br>you can find the python reference in mozilla here: <a href="http://developer.mozilla.org/en/docs/Python">http://developer.mozilla.org/en/docs/Python</a><br>and the book on mozilla platform: <a href="http://books.mozdev.org/html">
http://books.mozdev.org/html</a><br><br>cheers<br><br>Jorge<br>