CVE 2010-2764
Mozilla Firefox before 3.5.12 and 3.6.x before 3.6.9, Thunderbird before 3.0.7 and 3.1.x before 3.1.3, and SeaMonkey before 2.0.7 do not properly restrict read access to the statusText property of XMLHttpRequest objects, which allows remote attackers to discover the existence of intranet web servers via cross-origin requests.
See the 
CVE page on Mitre.org
for more details.
