It may just be my system (Windows, Firefox), but the jump key only worked sporadically. (Both X and K, and not even while moving or doing something else: I'd stand in one place and just hit the X key repeatedly, and it'd jump every fourth or fifth press.)
Also, when I got to the end of Level 1, the cloud collected in the jar, and then...nothing. No key presses or anything else seemed to do anything.