This indicates an attempt to exploit a remote vulnerability in Mozilla Thunderbird/Seamonkey/Firefox.
Multiple vulnerabilities have been identified in Mozilla Firefox and SeaMonkey. They can be exploited by attackers to bypass security restrictions, disclose sensitive information, cause a denial of service or take complete control of an affected system.
Mozilla SeaMonkey versions prior to 1.1.9
Mozilla Firefox versions prior to 220.127.116.11
Mozilla Thunderbird versions prior to 18.104.22.168
Denial of Service.
Update to Mozilla SeaMonkey version 1.1.9.
Update to Mozilla Firefox version 22.214.171.124.
Update to Mozilla Thunderbird version 126.96.36.199.