Although I suspected when I saw the control instructions, I wasn't going to comment on the firing mechanism until you fixed it so that I could check. Now that you've fixed the mouse fire, I have to ask (as I seem to be making a habit of on every platformer game on this site): What's with the tendency game makers on this site have for using the mouse to fire weapons that don't need aiming?
To be fair, yours works better than most, since you use the arrow keys for movement which is something most don't seem to even consider. Arrow keys don't trigger the delay built into my laptop to protect against accidental touchpad taps while typing, which means fire actually *works* unlike most platformer game on here, but it's still an awkward control.