The "Feed Preview" feature in Mozilla Firefox 2.0 before 2.0.0.1 sends the URL of the feed when requesting favicon.ico icons, which results in a privacy leak that might allow feed viewing services to determine browsing habits.
http://www.vupen.com/english/advisories/2008/0083
http://www.vupen.com/english/advisories/2006/5068
http://www.us-cert.gov/cas/techalerts/TA06-354A.html
http://www.ubuntu.com/usn/usn-398-1
http://www.securityfocus.com/bid/21668
http://www.novell.com/linux/security/advisories/2007_06_mozilla.html
http://www.novell.com/linux/security/advisories/2006_80_mozilla.html
http://www.mozilla.org/security/announce/2006/mfsa2006-75.html
http://securitytracker.com/id?1017421
http://security.gentoo.org/glsa/glsa-200701-02.xml
http://secunia.com/advisories/23672
http://secunia.com/advisories/23614
http://secunia.com/advisories/23589
http://secunia.com/advisories/23545
http://secunia.com/advisories/23282
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c00771742