Quite neat. I wouldn't use this myself as I prefer to have an environment which is crash proof and I would be too scared to close the window, however I think this could be quite great as an embedded editor.

It seems like the \pagebreak is not respected when printing on Safari (Chrome works fine). The preview shows a dotted line but the printed pdf is not broken.

Also, the footnotes are not on the correct page but always at the end. (This is on all browsers)