dkd903 (1156359) writes "If for some reason you were thinking of sticking with Firefox 4 and not upgrading to Firefox 5, well, don't. Mozilla has confirmed that Firefox 4 has reached its end of life and there will be no more security updates.
Mozilla released Firefox 4 only three months ago. After the release, there has been one update — Firefox 4.0.1 — meant to fix some secuty flaws. That is the last update the Firefox 4 will be getting. According to Daniel Veditz, Security Lead at Mozilla, Firefox 5 is the security update to Firefox 4."
Link to Original Source