JavaScript is responsible for many of the advanced website features seen today and increasing complexity can present performance issues.  Not all website browsers are created equal and there are clear winners in terms of JavaScript performance.  In order of best to worst performance:

That's right, the current release of Internet Explorer trails far behind the competition.  Version 9 appears to be addressing this deficiency which should provide ample reason to upgrade when the full release is available.

View the speed results yourself: