Mozilla has announced that after more than two years of support, Firefox 3.6 will no longer receive updates as of April 24. The legacy version of the browser is notable for being the final version before the company embarked on a radically different production path in 2011 with Firefox 4.
Barring any last-minute security patches, last month's Firefox 3.6.28 will be the final update that the 3.6-branch receives. Organizations like businesses and universities are being encouraged by Mozilla to switch to the Firefox Extended Support Release, which will allow them to update annually. The current version of Firefox, which is based off of Firefox 4, updates every six weeks.
Mozilla also revealed that it will stop supporting Firefox on computers running Windows XP Service Pack 1 and older, including Windows 2000, as of the June release of Firefox 13. This means that if you're on Windows XP, you ought to upgrade to at least SP2 -- although, SP3 is the most current service pack.