I uploaded thunderbird 0.9-6 to debian unstable and
released my new testing release to my
preview archive.
This release features a
new browser integration debconf mechanism
during the first installation to allow choose what kind of
browser integration is wanted.
A dpkg-reconfigure mozilla-thunderbird will allow you to change
your settings afterwards.
Currently available Browser integration mechanisms are
Debian,
GNOME, Manual. See this
FAQ entry for more info
about this.