Add the Swiftfox repository
sudo gedit /etc/apt/sources.list
Add this line at the bottom
deb http://getswiftfox.com/builds/debian unstable non-free
Update apt sources
sudo apt-get update
Check your CPU compatibility here
Install your version of Swiftfox
sudo apt-get install swiftfox-pentium4
Run with
Programs > Internet > Swiftfox