Thunderbird does not need to be installed as such. Simply get the tar ball from mozilla.org, and extract it somewhere like /usr/local/thunderbird. Then the program to run would be /usr/local/thunderbird/thunderbird.
I would suggest creating a symbolic link in /usr/bin:
ln -s /usr/local/thunderbird/thunderbird /usr/bin
Then you can start thunderbird by running the command "thunderbird"