Slightly Interesting Javascript Benchmark

I have an Asus CG5275 desktop, and decided to try out the Mandelbrot JavaScript benchmark at http://alexey.radul.name/ideas/2013/cleverness-of-compilers/ with the three browsers I use most, Chrome 29.0.1547.57, Firefox 23.0, and Opera 12.16. I expected Opera to be the slowest, and was not disappointed.

The mild surprise was that Firefox was almost four times as fast as Chrome. Here are my timings on the Asus with the above-mentioned URL and browsers:

Browser             Size    Time      Relative

Chrome 29.0.1547.57 500x500  9562 ms  3.86

Firefox 23.0        500x500  2478 ms  1

Opera 12.16         500x500 19464 ms  7.85

Opera took just about twice as long as Chrome, and Firefox was almost 4 times as fast as Chrome. This is on an Intel i5 at 3.2 GHz running Linux Mint 15, Mate, kernel 3.8.0-29-generic. It's a 4-core machine, which makes me curious about the almost 4x speedup of Firefox vs.. Chrome.

[ Note added about 15 minutes after original posting: Mate's System Monitor makes it appear that all three versions use just a single core. No real surprise--this is JavaScript, after all. ]