An easy way to install the new Firefox 3 beta 3 on Ubuntu is by using the terminal command below. But before jumping into it, you’re advised to backup your current user profile. This terminal command downloads and places a Firefox 3 folder in your home directory.
wget -P ~ ftp://ftp.mozilla.org/pub/firefox/releases/3.0b3/linux-i686/en-US/firefox-3.0b3.tar.bz2 && tar xjf ~/firefox-3.0b3.tar.bz2 -C ~
Note: This is a single line command.
An alternative way to backup your profile into a new folder rather than simple and manual copy and paste is using this terminal command;
cp -r ~/.mozilla/firefox/ ~/firefox_backup
The above command copies the Firefox profiles folder to firefox_backup in your home folder:
Also make sure you close any Firefox 2 windows before launching the Firefox 3 Beta 3.