Sunbird Mozilla Sunbird is a redevelopment of the Mozilla Calendar extension. Our goal is to produce a cross platform standalone calendar application based on Mozilla's XUL user interface language. At the moment the "Sunbird" name is a project name. It is not official and may change in the future. Our intended user is someone who uses Mozilla Firefox (or another browser) as his browser, Mozilla Thunderbird (or another mail client) as his mail client and wants a calendar application based on Mozilla. In addition, by focusing solely on standalone calendar, we believe we can make some dents in the overall footprint and performance of the calendar application by removing components and chrome we don't need. At the moment Sunbird is in an experimental stage. Although it is quite stable, we recommend it for testing purposes only.