CVE 2007-0780
browser.js in Mozilla Firefox 1.5.x before 1.5.0.10 and 2.x before 2.0.0.2, and SeaMonkey before 1.0.8 uses the requesting URI to identify child windows, which allows remote attackers to conduct cross-site scripting (XSS) attacks by opening a blocked popup originating from a javascript: URI in combination with multiple frames having the same data: URI.
See the 
CVE page on Mitre.org
for more details.
