I filed a couple bugs, relating to the matter:
And to my delight this new patch completely resolves all of them. Let's take a quick peak at the results. These are the results of doing
setInterval(fn, 0); in Firefox 2, Safari 3, Firefox 3, and Opera 9. Firefox 3 is in the bottom-left corner, note the improvement.
The change in quality is startling. It's easy to say that Firefox 3 and Safari 3 are quite comparable now, in terms of overall timer quality and, if nothing else, a major improvement over the timers in Firefox 2.