It's because currently FractalViewer is not designed to work around floating point precision limits in JavaScript. So, after zooming a bit, you hit the "pixelated wall". I plan to address this issue in future release of FractalViewer. See https://github.com/valera-rozuvan/FractalViewer/issues/10 .

More information on JS floating point numbers, their limitations, and ways to work around those limits - can be found in this informative article http://blog.chewxy.com/2014/02/24/what-every-javascript-deve... .