A system provides customized user interface data to a media application, such as a media discovery interface, or to any application for that matter, thereby extending the original application. Via a network connection, elements of a menu in a user interface can be downloaded to the application in a package of resources, including images, text, and links. A user interface framework of the media application processes a menu markup data resident on the local computer system and utilizes packaged resources, local code components, and externally-obtained (e.g., Web resources) to render a customized menu for the media application.