After a standard system upgrade you need to restart Firefox to effect the necessary changes.
Details follow:
Kojima Hajime discovered that Firefox did not properly handle an escaped null character. An attacker may be able to exploit this flaw to bypass script sanitization. (CVE-2008-5510)
Wladimir Palant discovered that Firefox did not restrict access to cookies in HTTP response headers. If a user were tricked into opening a malicious web page, a remote attacker could view sensitive information. (CVE-2009-0357)