Window does not fit on "high def" resolution monitor. This is a pretty major issue - you want the web play version to be sized so people with bad screens can play, and this means even decent screens are too small!
Like I said, try using browser settings to zoom in/out. 80% zoom worked for me and I have 1920x1080p. Also the frame size is actually 1920x1080p but because of the way the iframe is rendered it takes way more space