Mozilla has released Firefox 21 that closes eight security vulnerabilities including four High level and three critical security flaws.
Critical vulnerabilities : Memory corruption found using Address Sanitizer(MFSA 2013-48 ), Use-after-free with video and onresize event(MFSA 2013-46), Miscellaneous memory safety hazards ( MFSA 2013-41).
High level vulnerabilities: Uninitialized functions in DOMSVGZoomEvent( MFSA 2013-47), Mozilla Updater fails to update some Windows Registry entries( MFSA 2013-45), Local privilege escalation through Mozilla Maintenance Service ( MFSA 2013-44 ), Privileged access for content level constructor(MFSA 2013-42).
Firefox 21 introduces new feature Social API that "makes it easy for your favorite social providers to add a sidebar with your content to Firefox or notification buttons directly on the Firefox toolbar."
It also introduces Health report that "logs basic health information about your browser and then give you tools to understand that information and fix any problems you encounter".
Users are advised to upgrade the firefox as soon as possible, you can check version and update your browser by selecting to Help->About firefox.