CVE 2011-2366
Mozilla Gecko before 5.0, as used in Firefox before 5.0 and Thunderbird before 5.0, does not block use of a cross-domain image as a WebGL texture, which allows remote attackers to obtain approximate copies of arbitrary images via a timing attack involving a crafted WebGL fragment shader.
See the 
CVE page on Mitre.org
for more details.
