A nice post by the name "Forcing Thunderbird to open links in Firefox"
This post talks about how to specify / force Thunderbird to open links in Firefox in Ubuntu. For sometimes now, I had this problem of not being able to directly open links from Thunderbird. The same effect can be achieved if we do the following.
The real problem was that I had not specified the default system browser in System Preferences.
Go the Preferred Applications and specify the browser (Chrome/Firefox/Opera/Konqueror/ etc)
Open Thunderbird and all your links will now be opened in your default browser.
HOPE THAT HELPS SOMEONE OUT THERE