I've just tested on Chrome and it works great. Much faster and more difficult!
I love the enemy movement. Would love to see some more types of enemies and unique movetypes.
I'm sure you've already thought of this, but upgrades other than ammo and health (such as permanent increases or new weapons) would be extremely fun to create.
My only wish is that I can click on the upgrades rather than having to press keys.
Really nice work on this one mate, keep it up!