If at 60pixels/sec it's moving at 2 pixels per frame sometimes then your graphics card isn't really supported by browsers. I probably have the same issue with my blacklisted card, which never can reach 60fps with html5 on browsers even though normal exe games can.
Basically there are three things that could be at fault: C2, the browser engine, your machine.
You've likely played those retro games you mentioned on your machine without issue, your PC is capable so we can rule that out.
So I revise my statement to say that I think browser's renderer's are to blame.
This isn't a call for a native exporter, but if the renderer could be replaced things might improve. I say that as if it's easy, but it's probably way to hard to do. Especially since browsers can take so long to compile.
Anyways in the end I lack anything really helpful here.