While Mozilla has yet to announce the official changelog for Firefox 21, as TNW points out, the beta release notes give some insight into what to expect. For the desktop version, Mozilla have implemented three-state Do Not Track (
adding in a third option for "user says track"), added a suggestion system for improving app startup time, and implemented the
Firefox Health Report. For Android we should be seeing an updated UI based on the 'Holo' design, the ability to save media files, plus numerous bug fixes and enhancements.
