Probably because its being run with the internet. I downloaded your game and ran it. I didn't seem to have any problems. Either way, I like your game and think it has a lot of potential. You should keep working on it...

Another thing i just found, after one loses, the barrels still fall, which is fine, but the lighthouse(s) still fire rockets, which isn't really that good. it is however an easy fix...

This game is cool, but the bullets should be slower, the ships should be added at the edges, not in the middle, and the bullets should be able to destroy each other.