Very impressive, but performance sucks, even in google chrome. Keep in mind that the 486 is capable of fully emulating the NES. The truth is that javascript will simply never be appropriate for tasks such as this. It is too slow and no amount of magic fairy dust optimizations will make it come close to high performance languages.

Java on the other hand (as much as I hate java) can do high performance stuff. Here is a java applet NES emulator, with sound: http://www.nescafeweb.com