A message box will display the number of milliseconds taken when the number of runs is reached. Keep in mind that each non-blocking run adds a 16ms delay with setTimeout.
The result is just the total time, not a median. If you want to get a usable result, your best bet is running the benchmark multiple times and calculating the median yourself.
Firefox is fastest with pure processing (by a wide margin), but has problems with too many function calls and doesn't use the 16ms pause quite as well as Opera.
switch/1:1196ms switch/2:8470ms callback/1:3620ms callback/2:10108ms
Chrome is slower than Firefox, but still a lot faster than Opera. However, it's totally incapable of making good use of the 16ms pause.
switch/1:2787ms switch/2:9669ms callback/1:3279ms callback/2:10514ms
Opera does very well using the 16ms between runs, but is otherwise slow.
switch/1:7790ms switch/2:8284ms callback/1:8976ms callback/2:9942ms