This canvas demo is inspired by challenge on Atari ST to display as many sprites as possible at 50Hz (record is 312, every step of this saga is described and explained with passion on Leonard's page).
On my laptop Firefox3.6.6 can only display up to 200 sprites at 50Hz,... and Chrome6.0 more than 1000.
Maybe you could optimize code to obtain better results with other calls than drawImage?...