Secunia Research has reported a vulnerability, which affects most browsers. The vulnerability can be exploited by a malicious web site to "hi-jack" a named browser window, regardless of which web site is the true "owner" of the window.
You can find a test on their website: http://secunia.com/multiple_browsers_window_injection_vulnerability_test/ 
My question is now: How can we protect our websites for this vulnerability? Ok, we can wait until a bugfix will be available for all browsers. Should we test every second if the opened window is from the same location as we started?