Here are the steps, that you can also find here:
command line, as normal user:
echo "deb http://switch.dl.sourceforge.net/project/ubuntuzilla/apt all main" | sudo tee -a /etc/apt/sources.list > /dev/null
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com C1289A29
synaptics package manager
- update
- install ubuntuzilla
command line, as normal user
ubuntuzilla.py -a installupdater -p thunderbird
ubuntuzilla.py -a checkforupdategui -p thunderbird
ubuntuzilla.py -a install -p thunderbird
It took about 5 minutes all the process, then restarted thunderbird, and all is fine, and I'm happy!!