Doesn't work for me on Yosemite

OK, so it actually works just fine ??

And how large is the screen in real cm or inches?

If you want FancyBox to show on that screen size, replace the snippet with:

<script type="text/javascript">
var pixelRatio = window.devicePixelRatio || 1;
if(window.innerWidth/pixelRatio < 640) {
  	easy_fancybox_handler = null;
};
</script>

(note the 640 instead of 641 there, but you could go lower if you want…)

Real inches diagonal are 13″.

OK, I replace the original snippet. Mission completed! Thanks!

And thank you for your kind contribution! ??