It seems Firefox was part of the culprit, go figure.
I didn't get much use out of jumping, especially since the entrance to the third gate has so many puddles I basically couldn't jump enough to avoid them all.
The canvas loads really small and cuts off part of the game UI. Trying to hold the mouse button while hitting separate numbers for attacking is also incredibly awkward, likely for most people. It almost feels like you have a left-handed mouse and a number pad at your disposal, but I can't use my work computer to test this idea.