My unfinished shooter (running slow on web)

I have this fire elemental character from my webcomic that I’ve put in some animations, and now I’m putting him in his own web game.

The idea is pretty simple. Two types of “demons” come in from the right and you shoot fireballs at them. W.A.S.D. keys move Burnie (the fire elemental), and the mouse moves the crosshair. Hold down on the mouse to charge up a fireball and release to throw it towards the crosshair.

Throwing fireballs costs “mana” (the red bar), getting hit costs “life” (the yellow bar). Charging up a big fireball that can go through several demons is more cost-effective than throwing little fireballs at each one. Especially since demons drop “mana” if you hit more than one with the same fireball. Demons also burn when they are hit. If they touch another demon while burning, that demon will burn up too. Chain-reacting demons drop “life” for you to pick up. You can get some awesome chain reactions near the end of the time limit.

The twist is that you are trying to stay alive while preventing the bat-like “mailer-daemons” from getting to the left edge of the screen. If one gets past you, it causes a huge boss-demon to come and attack you.

The boss battle is still a little buggy, but it is possible to kill it. You have to aim for the eye (duh)

Anyway, here’s the game.

Let me know what you think. My main concern is that it runs really slow on some computers. Any ideas of how to improve speed? The animations run at 31 fps. I could probably reduce that to 12. Any other suggestions would be awesome.