New ubuntuzilla apt repository has been created for your convenience.
Now, instead of installing the script, then using the script to install, you can add the ubuntuzilla repository to your sources.list and use apt-get install to directly install firefox, thunderbird, and seamonkey.
For more details, see the ubuntuzilla website, in the "installation" section:
Current users of ubuntuzilla should run "ubuntuzilla.py -a remove -p yourpackage" before installing these packages, to undo the local diversion of /usr/bin/(package) links.
Please let me know if you run into any trouble with it.
...Edited to reflect the latest info.