You test your browser and see if it fails too. If it passes you will see
The page cannot be displayed
http://secunia.com/multiple_browsers_idn_spoofing_test/
I just tested using
FAILED
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.5) Gecko/20041107 Firefox/1.0
PASSED
Please post your results below.
Edit - Of course, for those that don't already know you can always avoid the spoofing problem by never trusting links. Always hand type your trusted web address in the address bar. Still FireFox has an over all security rating of moderately critical with 8 Secunia Advisories vs. IE as highly critical with 77 Secunia advisories. 