Here is a quick guide on how to upgrade Thunderbird 2 that comes with Ubuntu 9.10 Karmic Koala to glorious Thunderbird 3. Hopefully this will save some lost souls out there. :)
Open Terminal and copy folder ~/.mozilla-thunderbird to the new location expected by Thunderbird 3:
copy ~/.mozilla-thunderbird ~/.thunderbird
All emails, settings and extensions in ~/.mozilla-thunderbird will be your backup.
Get Ubuntuzilla package signing key to your keyring:
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com C1289A29
Add Ubuntuzilla repositories to the list of your sources either by using main menu System > Administration > Software Sources on the Other Software tab:
deb http://switch.dl.sourceforge.net/project/ubuntuzilla/mozilla/apt all main
Hit Reload button when asked to update software list.
Alternativelly the above step can be done with the following two commands in your terminal:
echo -e "\ndeb http://switch.dl.sourceforge.net/project/ubuntuzilla/mozilla/apt all main" | sudo tee -a /etc/apt/sources.list > /dev/null sudo apt-get update
And finally you can install the latest version of Thunderbird by running the following command:
sudo apt-get install thunderbird-mozilla-build
Don’t forget that you can erase the folder ~/.mozilla-thunderbird if the upgrade was successful. Have fun using the best email client in the world – Thunderbird 3! You can find it in the main menu Applications > Internet > Mozilla Build of Thunderbird.