Rearranging is quite fine, it's crossfade and zoom that is very jerky on my notebook.
I suspect it could be something about transparencies.
Firefox has long tradition of slowdowns when dealing with alpha-channel transparency, especially when compositing multiple transparent layers (also this demo uses "text-shadow" CSS property which puts additional load on renderer).
Unfortunately not in Firefox, at least for me (FF3.6 / Win7).
Especially this test was horrible:
http://razorjack.net/quicksand/demos/one-set-clone.html
Chrome, Safari and Opera performed much better. Even Explorer had smooth animation, though alpha-channel transparency animation there is broken.