XULRunner applications, extensions, and themes all share a common directory structure, and in some cases the same bundle can be used as a standalone XULRunner application as well as an installable application extension.

Basic Structure of a Bundle

A bundle may include any of the following files:

 /install.rdf                        Extension/Theme Install Manifest
 /application.ini                    Application Launch Manifest
 /components/*                       Component and XPT Files      (>=1.7)
 /defaults/preferences/*.js          Default Preferences          (>=1.7)
 /plugins/*                          NPAPI Plugins                (>=1.8)
 /chrome.manifest                    Chrome Registration Manifest (>=1.8)
 /chrome/icons/default/*             Window Icons                 (>=1.8)

Of course, an extension need not (and normally won't) have all of these directories. Themes are limited for security reasons, and can normally only provide a chrome.manifest which registers the theme and a JAR file.

See Also XUL Platform-specific Subdirectories, XUL Application-specific Extension Files