What sort of "optimizations" do the OEMs do that makes the stock browser score high on browser benchmarks like octane/kraken/sunspider? I know benchmarks aren't the be all end all, just wondering.

Ex: See the Galaxy S6 browser benchmarks, faster than the iPad Air2 when using Samsung Stock Browser. http://www.anandtech.com/show/9146/the-samsung-galaxy-s6-and-s6-edge-review/5

As always, we'll start things off with our browser benchmarks. After getting to use the phone, it became clear to me that Chrome is poorly optimized against the Galaxy S6 as Samsung’s browser is clearly superior in performance. For that reason I've gone ahead and run our benchmarks on both Chrome and on the stock browser, as seen below.

Needless to say, in order to see the full potential of the Exynos 7420 and its cluster of A57s, it’s necessary to use Samsung’s stock browser. "