It doesn't work at all for me in Firefox 3 on Windows. I get the same response after clicking on all links (feed reader, HN frontpage, this page):
Page Load Error
Address Not Found
Firefox can't find the server at www.➡.ws.
This is the same trouble as with Unicode snowman domain.
In one discussion here on HN I figured out it's probably because of some security measure to prevent phishing. There are some Unicode characters that look like normal ASCII letters (for example in Cyrillic alphabet), so if Unicode worked in urls, you could create malicious sites that would look like real ones: