The CheckLoadURI function in Mozilla Firefox 1.8 lists the about: URI as a ChromeProtocol and can be loaded via JavaScript, which allows remote attackers to obtain sensitive information by querying the browser's session history.
https://bugzilla.mozilla.org/show_bug.cgi?id=371375
http://www.securityfocus.com/archive/1/461013/100/0/threaded
http://www.securityfocus.com/archive/1/461006/100/0/threaded
http://www.gnucitizen.org/projects/hscan-redux/