Ok, so, probably my laptop is the problem :)
In C2 I see a nice 1 px black line around each side of each block.
When I press play, I can see some blury black pixel around left side and not any black pixel around right side.
Maybe these images will explain more.
What I get in C2 :
<img src="http://img542.imageshack.us/img542/9715/24141804.jpg" border="0" />
What I get in FF/Chrome
<img src="http://img18.imageshack.us/img18/1765/85450731.jpg" border="0" />
I hope you can see the difference now. If not, I'm a crazy guy, haha.