setInterval very slow in browsers?

I am making a Flash game, and the level moves depending on how far away you are from the center of the stage. I have to put these actions in a function called by a setInterval method because each level is an individual frame. I have the interval set to call the function every millisecond. It works fine in the standalone Flash Player, but when I put it in an HTML file it goes very slow. I have tested it in Firefox and IE7. Any help?