For those of you using Prototype 1.6 (or Magento prior 1.6), you might wonder why event.stop() or Event.stop(event) doesn’t work in Internet Explorer 9. Here’s a quick explanation:
IE 9 makes major changes to the event system. We had to rewrite the
event code in 1.7 to support it. You can either (a) upgrade to 1.7;
(b) force your site into compatibility mode .
So it’s been fixed in 1.7, but what if I can’t upgrade to 1.7 and don’t want to render my website in compatibility mode? Well, after a couple of hours trying to sort this out, here’s quick (and dirty) patch for Prototype 126.96.36.199. Download Prototype 188.8.131.52 Event.stop IE9 fix (448 bytes)
Also, for further reading, here are two external links that you might find useful for this issue.
Note/Disclaimer: This has only been tested on Prototype 184.108.40.206. Use it at your own risk.