In a word: choice. Which is the original point of Linux, I believe. I couldn't comment on the functionality of any RO browser, but Google seems to disagree with you, BTW.
If I appear to keep going on about hardware multi-threading, it is only to establish what we are discussing. I have no interest in hardware multithreading, except to determine whether it is likely to appear on ARM in the near future (I think not).
But structuring code in a way that allows many separate routines (threads) to run independently (which I have called multi-threading) is the way to take full advantage of multiple processors. In my original post, I have suggested several ways this could be achieved.