Fx4b6 does not include the new JaegerMonkey javascript engine, so the lack of a speedup compared to Fx3.6 is not terribly surprising.<p>JaegerMonkey is in Fx nightly builds at the moment and is supposed to be featured in Fx4b7 (to be released later this month).
Note that it's an "user drags something in the UI and we measure something" benchmark, so it's potentially suspicious if the things measured are comparable at all in different runs and browsers.<p>For example, in games, frames per seconds are measured under basic assumption that the game has the mode in which there's no limit the increase of frames per second other than the speed of rendering and that that mode is always identically reproducible.<p>Are we sure about that here?<p>And as others noted, they are using the old version of Opera, 10.53 instead of 10.62 which is current.
As an interesting comparison, I just saw that John Resig posted a benchmark of jQuery.css() performance across browsers. It doesn't include IE9, but does include Opera 10.62 and FF 4.0b6 - <a href="http://www.flickr.com/photos/jeresig/4999526752/" rel="nofollow">http://www.flickr.com/photos/jeresig/4999526752/</a>