CVE 2007-2869
The form autocomplete feature in Mozilla Firefox 1.5.x before 1.5.0.12, 2.x before 2.0.0.4, and possibly earlier versions, allows remote attackers to cause a denial of service (persistent temporary CPU consumption) via a large number of characters in a submitted form.
See the 
CVE page on Mitre.org
for more details.
