This indicates an attempt to exploit a vulnerability present in Apple QuickTime when used with Mozilla Firefox.
The vulnerability is a result of a flaw that allows XML files disguised as QuickTime media format files to hack into Mozilla Firefox. A remote attacker can exploit this to execute arbitrary programs and may be able to gain complete control of the system.
Apple QuickTime and Mozilla Firefox.
System compromise: execution of arbitrary code on the system.
Currently we are not aware of any official fix for this issue.