Secunia Research has reported a vulnerability in multiple
browsers, which can be exploited by malicious people to
spoof the content of websites.
The problem is that a website can inject content into
another site's window if the target name of the window is
known. This can e.g. be exploited by a malicious website
to spoof the content of a pop-up window opened on a
trusted website.
Secunia has constructed a test, which can be used to
check if your browser is affected by this issue:
http://secunia.com/multiple_browsers_window_injection_vulnerability_test/