CVE 2009-3979
Multiple unspecified vulnerabilities in the browser engine in Mozilla Firefox before 3.0.16 and 3.5.x before 3.5.6, SeaMonkey before 2.0.1, and Thunderbird allow remote attackers to cause a denial of service (memory corruption and application crash) or possibly execute arbitrary code via unknown vectors.
See the 
CVE page on Mitre.org
for more details.
