If you want the latest Thunderbird in Ubuntu open up terminal and type the following (copy and paste from here if you want)
sudo apt-get update
type your password there when prompted to, then after is done doing its thing type
sudo apt-get upgrade
let it finish and I then open Thunderbird and it should have the latest on it. Try that and if it doesnt work report back and we can figure out another way.
For the migration here a thread with a similar question http://forums.mozillazine.org/viewto...f=39&t=1119095
Good luck to you!