As chachazz has pointed out, the latest Fx ESR version was released in November 2012. Fx 10 ESR was originally released in Feb 2012 and will no longer be supported as of February 2013. There is an overlap of approximately three months when both versions are supported. This is done so that enterprise users have some time in which to test the new version (while the current version they have is still supported) before deploying within their company.
I would have upgraded in November except that is when I got a new computer with Windows 8 and had enough on my plate trying to get used to Win 8 that I did not want to also have a new browser version (with no multiple profiles like it has been forever with Fx and other changes that would seem big to me) to get used to so I decided to take advantage of the approximately three month overlap and use the older ESR version during the overlap time. -- When governments fear people, there is liberty. When the people fear the government, there is tyranny. Thomas Jefferson