Name: Mbox2XML
Website: http://tools.elit.nl/mbox2xml.php
License: Freeware
Description: (taken from website) Mbox2xml is an email archiver for Mozilla Thunderbird, which extracts messages from the mbox format used by Mozilla Thunderbird and stores them in an XML format, which can be viewed as web pages in a browser.
Notes: Just tried this app. It is amazing! Finally, a way to back up all your e-mails externally and browse them easily in any web browser! It even keeps all attachments. Absolutely the most useful tool of 2011.
It currently has a no-install version (zip) and except for MRUs, it doesn't appear to leave registry entries. Also does not appear to leave any local user folder files; settings are written to gui.ini in the app directory, which does save paths with drive letter, but this might be able to be dealt with by the PAL...