Unfortunately even a great language can become a nuisance if its working environment is web browsers. Since the browser war started between MSIE and Netscape more than a decade ago, all major browsers try to be a bit different, but that wouldn’t be a problem in itself. This only started to take casualties once the browser makers with the biggest influence went against each other in what their browsers can do and how it does that, when it should work the same way for everyone. It’s generally accepted knowledge, that IE is buggy. Less people are willing to admit that Firefox is buggy as well. Even less about Chrome. (I won’t even start with the rumors about what these browsers do incorrectly on purpose.) Not just that, but even the “official” specifications can set ambiguous rules, that the different companies and organizations can and will interpret differently.
Update: Chrome and Opera never fires the mouseout / mouseleave events when mouse moves to a floating on-top window, firefox does randomly, while it always seems to work with IE. (There are things IE gets right and the others don’t.)