That won't cause it to be "blurry" -- that just causes it to be black. "Blurriness" is indeed due to floating-point errors in the coordinates system.
For me, in the browser, the edges just smooth out to a straight line, and seem blurry only because of the color scheme.
In the desktop version, however, I see this when zoomed in maximally: http://i.imgur.com/ryhai.png.
Ah, fair enough. It's probably the iterations then.
This is what I maxed out at. It did start to look blurry right before it started lagging, and these staggered lines were revealed, but they look much different from yours.
http://i.imgur.com/R5PbQ.jpg