Firefox Extensions

According to security researcher Christopher Soghoian many widely used Firefox extensions, including toolbars from Google, Yahoo, and AOL, do not use secure connections to update themselves. His research highlights that it is possible to leave users vulnerable to a "man-in-the middle" attack, which could trick Firefox into downloading malicious software from a site it mistakenly thought was hosting an extension.

http//paranoia.dubfire.net/2007/05/remote-vulnerability-in-firefox.html