[metajack]

Parsing is serial for a single source, but multiple things (CSS, HTML, multiple HTML files) can be parsed at the same time. Also, the thread running JS (which drives HTML parsing) is separate from another page's JS thread. There can be many of these per process unlike Firefox and (I believe) Chrome.

CSS matching and layout have fine-grained parallel algorithms built on top of work stealing queues. Rendering is handled totally on the GPU (as opposed to other browsers which just offload compositing).