Comment 15 for bug 373167

John, the reason why it looks like a Thunderbird bug is that it appears that the Thunderbird package installs a thunderbird and a mozilla-thunderbird link in /usr/bin, both pointing to /usr/lib/thunderbird/thunderbird. If you remove the mozilla-thunderbird link, it resolves the problem. So steps to reproduce:

cd /usr/bin
sudo ln -s ../lib/thunderbird/thunderbird mozilla-thunderbird

If you now go to System -> Preferences -> Preferred Applications, you will see both a "Thunderbird" option and a "Mozilla Thunderbird" one. If you remove the /usr/bin/mozilla-thunderbird link, the second option disappears from preferred applications.

It looks like the /usr/bin/mozilla-thunderbird link that is created when installing the thunderbird package is superfluous. Or is this the intended behaviour and does it mean that the preferred applications preference tool should show only one option even if both links are present?