Running the tests (http://codeflow.org/issues/timing/) on OSX as well, and this also reveals remarkably bad results once dropping below 60fps.
Chrome:
Firefox:
Note how here again frame times are clamped roughly between 16.6ms and 33.3ms (quite similar to chrome on linux). However unlike chrome on linux, these exhibit hysteresis all the way.
Safari:
It needs to be noted, that although the RAF curve for safari looks quite good, the display experienced by the user in this case is incredibly choppy (this is because uneven frame timings bust vsync/composition sync).