It's not very hard to crash a browser or browser tab. There's a certain point where all situations can't be reasonably handled by the browser, and it makes more sense to crash when something unexpected happens.

Here's an example I posted a while back of how to crash most major browsers with a link: http://blog.doteight.com/blog/2011/08/24/this-link-will-cras...

* Just checked, it only seems to work with Chrome these days. I guess the other browsers have figured that one out.