This indicates an attack attempt against a buffer overflow vulnerability in Mozilla Firefox.
The vulnerability is caused by an error when the vulnerable software handles a malcious font file. It allows a remote attacker to execute arbitrary code via sending a crafted web page.
Mozilla firefox 3.6 and other versions
System Compromise: Remote attackers can gain control of vulnerable systems.
Upgrade to the latest version beta build of Firefox 3.6.2. The full version will be available on March 30.