A user named   has posted a video on youtube comparing available browsers for N9.He has done HTML5 test for PR1.2 browser and the official version of Firefox and Opera mobile browsers.

The scores are,

PR 1.2 default browser – 271 + 14 Bonus points

Firefox – 315 + 9 Bonus points

Opera mobile browser- 245

Firefox seems to be the king of browsers as far as HTML5 compatibility is concerned.