How secure is your browser/computer if you happen on to a web page designed to cause you problems?
If you want to find out, you can take a look Here.
Note: the page is in Italian but if you set your browser to translate the page, the translation is good enough to understand what the author is talking about.
Warning 1: The tests are designed to stress either your browser or your computer. If you are vulnerable to the code in a particular test, your system may well lock up or crash. This is by design. And you will be clearly told before you get to any code that will cause problems.
Warning 2: Several pages have a trojan XMLid.exploit and use it to perform the stress testing. I Do Not know for sure that the pages are harmless except for the stated test purposes. Probably are but I'm not expert enough to know for sure. Here is what McAfee has to say about this particular trojan.
Opinion: This is the perfect page for any of your friends who never run AV software because, "I never open email attachments".