This indicates an attempt to exploit a Denial of Service vulnerability present in several of the most popular web browsers.
Multiple browsers (IE, Firefox and Opera) contain a DoS vulnerability. A remote attacker can exploit this vulnerability to consume all available CPU resources on a victim's system, via a specially crafted webpage.
Mozilla Firefox version 18.104.22.168
Mozilla Firefox version 22.214.171.124
Mozilla Firefox version 1.0.8
Opera Web Browser, any version.
Microsoft Internet Explorer, any version.
Denial of Service.
Currently we are not aware of any vendor supplied patches for this issue.