People should quit trying to make CSS a drawing tool--it is not--and start learning how to use SVG instead or images.
I wonder why the firefox CSS rendering engine prefers to smooth out. Looks like a dramatically different implementation, but maybe that's just because it's an edge case of rendering
Neat! It's unfortunate that the rendering is so different between browsers.
Have you tried the same thing with shadows? They can also be stacked, I believe.