The latest version, firefox 3.5 is the fastest firefox yet, it has many new features.
To install firefox 3.5,first add following two lines into /etc/apt/sources.list
sudo gedit /etc/apt/sources.list
deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu jaunty main
deb-src http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu jaunty main
Then add GPG key
sudo apt-key adv –keyserver keyserver.ubuntu.com –reckeys 247510BE
Update and install firefox 3.5
sudo apt-get update
sudo apt-get install firefox-3.5