I know you're probably not concerned with compatibility for Windows 7, but I thought I should post nonetheless. I'm running on Windows 7 and I have difficulty running and jumping at the same time (if I press down the run key, the jump key *usually* doesn't work; it will sometimes but is completely unreliable). Because of this I can't get past 2-1. I've tried on both Firefox and Chrome so I'm pretty sure it's not a browser issue. Other than that I really like this game!