Not sure what computer you ran the demo on, but the Unreal Engine demo on top of Chrome was unusable on my laptop (talking about 2-5 fps), whereas in Firefox it

Not sure what computer you ran the demo on, but the Unreal Engine demo on top of Chrome was unusable on my laptop (talking about 2-5 fps), whereas in Firefox it was extremely smooth and this was when Firefox 22 was released (so it was the stable release, not the nightlies). EDIT: I just ran that demo in Chrome, on the same computer as before and it did improve a lot (getting 50-60 fps in full screen HD), though it still seems smoother in Firefox. Competition is great.