Mozilla reports Firefox 2.0 contains a cross-site form bug that allows phishers to steal passwords out of the Password Manager.
To exploit the bug phishers need to run a form on the site where the password is meant for. One of the sites that is heavily affected by this bug is MySpace. The reporter of this bug says phishers are currently using it on MySpace to steal people's accounts.
When a MySpace users visits a profile created by one of these phishers he/she will get a perfect-looking MySpace login form that uses HTML and absolute positioning. However, this is not the real login form, it's hosted on another domain. Firefox doesn't raise a warning and even fills in the form with information from the password manager!
It's not sure whether Internet Explorer is also affected by this bug.