This indicates a possible attempt to exploit one of several vulnerabilities in Mozilla Firefox and SeaMonkey.
The vulneabilities are a result of memory corruption in the Layout Component. They may allow a remote attacker to crash the application causing a Denial of Service.
Mozilla Firefox before 18.104.22.168
SeaMonkey before 1.1.7.
Denial of Service: Remote attackers can crash vulnerable systems.
Upgrade to the latest versions: Firefox 22.214.171.124, SeaMonkey 1.1.7 or newer.