Prism is a simple XULRunner based browser that hosts web applications without the normal web browser user interface. Prism is based on a concept called Site Specific Browsers (SSB).

An SSB is an application with an embedded browser designed to work exclusively with a single web application. It doesn't have the menus, toolbars and accoutrements of a normal web browser.

Some people have called it a "distraction free browser" because none of the typical browser chrome is used. An SSB also has a tighter integration with the OS and desktop than a typical web application running through a web browser.