Adding features Extensions are generally used to add functions to the application. Examples of functions which an extension might add include RSS readers, bookmark organizers, toolbars, website-specific client programs, FTP, e-mail, mouse gestures, proxy server switching, web-search and -uploading functionality, retrieving keyword definitions or website-linked content, automated backups, media downloading, or developer tools. Many Firefox extensions implement features formerly part of the Mozilla Suite, such as the ChatZilla IRC client and a calendar.