This indicates an attack attempt against a memory-corruption vulnerability in Mozilla FireFox.
This issue is caused by an error when the vulnerable software handles "document.write()" methods and DOM insertion. It may allow remote attackers to execute arbitrary code by sending a crafted web page.
Mozilla Firefox version 3.6.11 and prior
Mozilla Firefox version 3.5.14 and prior
Mozilla Firefox version Thunderbird 3.1.5 and prior
Mozilla Firefox version Thunderbird 3.0.9 and prior
Mozilla Firefox version SeaMonkey 2.0.9 and prior
System Compromise: Remote attackers can gain control of vulnerable systems.
Refer to the vendor's web site for the suggested workaround: