https://sourceforge.net/p/ubuntuzilla/wiki/Main_Page/#installation
...and you can use the following command to add it to your sources.list in one step:
echo -e "\ndeb http://downloads.sourceforge.net/project/ubuntuzilla/mozilla/apt all main" | sudo tee -a /etc/apt/sources.list > /dev/null
> should become >
Also the section "Localizations" contains some > and < which need to be fixed.
Thanks, fixed! (It slipped my mind htere for a bit >_<)