Those guys over at Hotmail, at it again. Once more an essential bit of code is omitted from the page they send Opera.
If you use Opera, go to your Hotmail junk mail folder and click the "Empty" button, a window with "OK" and "Cancel" buttons appears. If you click the "OK" button nothing happens because that button points to something they forgot to include in the version Opera gets.
To get very technical: the function "jmfPf" is not defined in the <http://by16fd.bay16.hotmail.msn.com/cgi-bin/dasp/EN/hotmail___10000035110.js> library when accessing your site with Opera.
Wish they would move away from this fragile and badly implemented server-side sniffing solution and just use some decent object detection. Any script can adapt automatically to the capabilities of the browser it is running in, when written carefully.