One of the things you need to do is add the following line to your prefs.js file under your .thunderbird/xxxx.default directory:
Don't do this while Thunderbird is running otherwise you'll lose the changes.
The second thing I did was change the symbolic link for my kde browser under /etc/alternatives
lrwxrwxrwx 1 root root 26 Nov 21 14:49 webclient-kde -> /usr/local/firefox/firefox*
I deleted whatever was there previously and setup a link to firefox. (see http://www.die.net/doc/linux/man/man1/ln.1.html