Hey, I've just found this test that sorts browsers based on their performance/support of HTML5.
Develop games in your browser. Powerful, performant & highly capable.
Cap is 450.
Firefox 8: 314 and 9 bonus
Chrome 15: 343 and 13 bonus
Opera 11.6: 325 and 9 bonus
Hm... seems like Chrome is the best for HTML5, but i see alot of bugs on Chrome when making game, hope they fix soon.
In "other browsers" tab:
IE9 - 141 and 5 bonus <img src="smileys/smiley21.gif" border="0" align="middle" />
and the score of the IE10 which (if I remember correctly what Ashley said) should be in developement for one more year.
IE10 - 300 and 6 bonus
that's a shame