CVE 2011-2372
Mozilla Firefox before 3.6.23 and 4.x through 6, Thunderbird before 7.0, and SeaMonkey before 2.4 do not prevent the starting of a download in response to the holding of the Enter key, which allows user-assisted remote attackers to bypass intended access restrictions via a crafted web site.
See the 
CVE page on Mitre.org
for more details.
