Hello!
I had the jump height issue that the others also reported and managed to make a little patch to fix it. If you have this problem the game will seem a bit laggy and the jump height becomes inconsistent, usually less than two tiles.

1. Download the game and open the .html file in a text editor.
2. Scroll down to line 1559 and delete this line: "setTimeout( update, 1000/TICKS_PER_SECOND );"
3. Scroll to line 1563 and add "update();" just below "function render() {" 
4. Done!

If your refresh rate is higher than 60Hz then the game will run too quickly. I have a (untested) way to patch that too, but this comment box is really uncooperative.

For anyone interested here is a stackoverflow thread that explains this problem.