Version 10 of Firefox and Thunderbird were released on January 31. Several security fixes have been implemented.
With the release of Firefox version 10, Mozilla has also begun deployment of the Extended Support Release – https://wiki.mozilla.org/Enterprise/Firefox/ExtendedSupport:Proposal
The Extended Support Release will provide large organizations (such as Universities, Schools, City/State governments) additional time (when compared to Mozilla normal 8 week release cycle), for testing and deployment of new versions. Mozilla has currently proposed that the Extended Support Release versions will be supported for a period of 54 weeks. During that period, critical and important security patches will be applied to Extended Support Releases (and they will appear as point releases coinciding with normal version updates for Firefox and Thunderbird) However, other enhancements will not be back ported.
The link to download Firefox ESR (for various operating systems) is available at the bottom of the http://www.mozilla.org/en-US/firefox/organizations/faq/ URL.
Additional details about ESR is available at the following URLs
NOTE: A ESR version of Thunderbird is also available – information (including a download link) on the Thunderbird ESR version is available at: http://www.mozilla.org/en-US/thunderbird/organizations/faq/
Update February 2
Release notes for version 10 can be found at – http://www.mozilla.org/en-US/firefox/10.0/releasenotes/