[mathrawka]

From their development details (http://www.cuttherope.ie/dev/), this point stuck out to me:

With some guidance from Microsoft, we decided to replace the recursive function with an “unpacked” iterative version of the same code. The results were amazing. We saw a 10x improvement in every browser! Frankly, we would have never found that without the profiling tools in Internet Explorer 9.

[chucknthem]

To be fair, they probably could have found the same performance problem profiling using chrome or firebug