Versions of Firefox 4.0.x earlier than 4.0.1 are potentially affected by multiple vulnerabilities :
Multiple memory corruption issues could lead to arbitrary code execution. (MFSA2011-12)
Binary data 5902.prm
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0068
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0069
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0070
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0079
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-0081
cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2011-1202
www.mozilla.org/security/announce/2011/mfsa2011-12.html
www.mozilla.org/security/announce/2011/mfsa2011-17.html
www.mozilla.org/security/announce/2011/mfsa2011-18.html
www.mozilla.org/security/known-vulnerabilities/firefox40.html#firefox4.0.1