Aza Raskin, User Interface specialist and creative lead on Mozilla’s Firefox browser described a new type of phishing attack which he called "tabnabbing".

Tabnabbing exploits the fact that most users have multiple tabs open on their browser while browsing the internet. The attacker sends a link to a legitimate looking site. When the webpage detects that the user has moved to a new tab, the javascript code embedded in it 'changes' it to some login page. Unsuspecting users will most likely login to this fake page thinking they opened it and their account is compromised.

In his website, Aza Raskin has actually embedded such a script in this webpage
http://www.azarask.in/blog/post/a-new-type-of-phishing-attack/

Nice! Thanks for posting, that's pretty interesting

Apart from FireFox, it works with IE8 too, just checked it

That definitely has some potential to pwn people, especially if well executed.   We've all seen sessions expiring in gmail, yahoo, etc, for no apparent reason.   I am also careful to check the URL and the certificate when logging in, but I am sure people will be easily fooled by this.