Post the URL of the site. I will bet the site fails validation. It's just another of the many 'lame' sites that has a webmaster that either;
doesn't know what he is doing,
doesn't care,
gets paid by M$ (in one form or another) to write ONLY for Idiot Exploiter, blocking out any other browser.
It's NOT Opera!!!
BTW; You can right click on any page and choose 'Validate'. It will send you to the W3C validation page and give you the list of what's wrong with the page you are validating;
http://validator.w3.org/
and a less strick;
http://www.htmlhelp.com/tools/validator/