Yes, other engines do not seem to handle polymorphism well. I just amended the code to use separate test_something_arraytype for each array type. And, it turns out that the performance of other browsers have improved significantly and they look closer to Chrome now. Check out the updated charts in the blog post.
I suggest you add a note to the text hinting that you are not using original tests anymore. It would be even cooler if you publish both results of original (polymorphic) and your (non-polymorphic) runs.
I find results for "random read" particularly interesting. I need to take a look at the generated code. It might be that there is something in the way V8 compiles integer modulo operation that makes it slower than SpiderMonkey.
[though for this test to be comparable across browsers you should really fix function init_randlist not to use Math.random but use a pseudo-random generator with a _fixed_ seed. Uncontrolled sources of randomness should be discouraged in microbenchmarks and they lead to flaky unreproducible benchmarks. Though I don't think that it's the reason here].
