It's surprising that there is little or no focus on other, perhaps more relevant performance aspects of modern pages. For example, how do browsers perform when it comes to dynamically changing the style of a page (CSS)? …
Another related issue that I saw mentioned the other day was a rather flawed and narrow memory usage test which doesn't take into account how different browsers deal with memory in different ways. For example, it ignored Chrome's shared memory, and did not seem to be taking Opera's advanced memory cache into account.
Opera also cleans up the image cache after 10 minutes or so, but that does not seem to be reflected in the test. We could have done the cleanup all the time, but then we would have to sacrifice performance like Firefox apparently does.
It is basically a tradeoff.