Prism 是以 XULRunner 為基礎的極簡化瀏覽器，可以讓網際應用程式不必透過一般瀏覽器介面就能直接執行。Prism 的主要概念是「特定網站專用瀏覽器」，就好比為某個網際應用程式量身訂做的瀏覽器一樣，無需選單、工具列及其他傳統瀏覽器的元件。這類專屬瀏覽器能為其網際應用程式提供與作業系統更緊密的整合，所以能同時擁有一般單機程式與網際應用程式雙方面的好處。
- 分隔運作程序 Web apps can hog memory or processor cycles or even bring down the whole browser in extreme cases. By running each app in its own process, we minimize the impact of any mishaps. We can also benefit from operating system tools that less us view the memory/CPU consumption of a specific application.
- 使用介面極簡化: A general-purpose browser UI is not necessary or appropriate for most web apps. It is more efficient to provide a UI that is specific to the application. This also cuts down on UI clutter (hence the term distraction-free browser).
- 與作業系統整合: Support of desktop features can make using the app more natural and convenient for end users. This includes the ability to create desktop shortcuts, to place the application icon in the tray or dock and to display pop-up notifications.
- 專屬自訂方式: Apps can be run using a shared browser runtime and customized using client-side script (similar to Greasemonkey). Custom stylesheets can be used to tweak the UI.
Prism 是個 XULRunner 軟體，其中除了 XULRunner 內建的瀏覽器引擎外還包括：
- 網際軟體包管理: Code for creating new web app bundles and loading existing bundles.
- 捷徑建立介面: A dialog box lets the user specify attributes of the web app (name, URI, icon, shortcut locations).
- 作業系統整合功能: Binary components provided access to OS-specific features like shortcut creation and dock/tray icons. We intend to propose these extensions for inclusion in future versions of XULRunner.
- Firefox 擴充套件:: A Firefox extension, code-named "Refractor", can be used to spin out new Prism apps from inside the web browser. Refractor adds a new menu item to call up the shortcut creation dialog for inside Firefox. Web apps can also point to a complete web app bundle or some elements of a web app (like higher resolution icons). Refractor automatically takes this information into account.