I have tested this problem on both regular Firefox x86 from Firefox.com on Windows 7 x64 and two specially compiled 64-bit high-speed versions of Firefox called BlazingFast and Waterfox. I have also tested in Google Chrome. It works in Chrome pretty well. There is much less lag.
With much better compiled versions of Firefox, this should not be a problem, I feel. I would like someone to investigate further at WordPress.