There are a couple of sites which claim to test browsers. I've tried both but I have no idea what, if any, reliance can be placed on their results;
This one is a 'general' tester which is configured to work with IE so it gives rather odd results when I test Opera with it!;
http://www.b2knet.com/ while this one claims to check the security status of IE, Mozilla and Opera;
http://bcheck.scanit.be/bcheck/
Be sure to read all the instructions carefully if you decide to try the second one because it does try to crash (but not infect) your browser! I've never had problems with it but no two systems are exactly the same.