Version 21 of Mozilla Firefox  is now available, with version 20 of the browser released only last month. Included in the latest version is the addition of multiple social providers, enhanced three-state UI for Do Not Track, and plenty of other items. The desktop update is available for Windows, Linux, and OS X. Firefox is also rolling out a gradual update onGoogle Play for Android users.
The biggest change comes in the form of the social integrations, with Cliqz, Mixi, and MSN Now added to the social mix. The browser first added Facebook integration back in December, and the inclusion of these services goes a long way towards making social integration an even larger part of the services offered.
If you’ve never heard of these services, allow me to explain them for you. Cliqz is designed as a place for users to find articles, stories, and videos based on your interests. Mixi, which is only available in Japan, is a social network. MSN Now is a place for users to find out what kinds of things people are talking about on the Web.
If you want to customize your Do Not Track status, the new version includes a three-state Do Not Track option: don’t track, track, and do nothing The update also includes some improvements to the way the browser handles HTML 5, specifically support for the <main> element and scoped stylesheets.
On Android, the main part of the update comes in the form of custom open source fonts Charis and Open Sans. It also adds the ability to save media files with a long tap, a new Holo interface, and other performance tweaks.
What’s your favorite feature in Firefox 21?