Prism is a project by Mozilla to produce an application more geared towards web applications such as Google mail. It’s light doesn’t contain any buttons such as back/forward and allows you to concentrate on the application itself, providing better desktop-web integration to the user. If you would like more detail regarding Prism see Mozilla Labs.
First download Prism to your Desktop. Then right click on the .tar.bz2 and select extract which will give you the folder prism. I then moved the directory to my home directory. For example in the terminal:-