timer in JS without getting error in js

Question

I would like to add a js window.setInterval timer to a page, but Firefox gives me a warning message:

"A script on this page may be busy, or it may have stopped responding. You can stop the script now, open the script in the debugger, or let the script continue."

window.setInterval(function() {
    doSomthing();
    }, 500);

Is there a technique to avoid this message?