Memory leak in Libxul, as used in Mozilla Firefox 3.0.5 and other products, allows remote attackers to cause a denial of service (memory consumption and browser hang) via a long CLASS attribute in an HR element in an HTML document.
https://exchange.xforce.ibmcloud.com/vulnerabilities/47758
http://jbrownsec.blogspot.com/2008/12/new-year-research-are-upon-us.html