XULRunner is a Mozilla runtime package that can be used to bootstrap XUL+XPCOM applications that are as rich as Firefox and or Thunderbird. It is similar to other existing runtime applications such as J2SE Java Runtime Environment (JRE). It enriches desktop application with provides an innovative integration concept and allows technology that developers can use to write enrich and integrate their desktop applicationapplications.

This runtime package provides a way for installing, upgrading, and uninstalling XULRunner applications. XULRunner will also provide libxul, a solution which allows the embedding of Mozilla technologies in other projects and products. These applications can be written in any Mozilla supported technologies by Mozilla web platform. Some of these technologies are the following: