FF and Chrome won't allow me to stop unresponsive script

FF and Chrome won’t allow me to stop an unresponsive script, that is, a popup doesn’t appear that gives me the choice. I’m learning from Kevin Yank’s Learnable video on JS and there’s a simple JS file where he demonstrates debugging, but when I edit it and refresh my page, I just get the Mac colored pinwheel and the popup that would normally appear, never appears. Seems that now Firefox has finally displayed the popup but not Chrome. FF did it after about 4 or 5 minutes, which means that, at this rate I’ll never get my script debugged. Is there some way to stop an unresponsive script sooner in FF, or to even stop it at all in Chrome?
Thanks.
R

I think it would help posting the script here…

In Chrome (or Safari or Opera or Internet Explorer) you can use the built in debugger to track exactly what the script is doing - statement by statement if that’s what it takes but usually setting a few breakpoints would soon help you work it out. In Chrome press F12 to bring it up.

In Firefox you need to install an extension that provides a debugger - Venkmann is one that looks the same as the debuggers built into all the other browsers. Firebug can also be used but looks a bit different to what you would see in the other browsers debuggers.

The problem is not the script itself. I’m just trying to learn to use the Chrome debugger and I can’t stop the script to debug it. I know the script problem, I just want to use the debugger in the future for my other scripts, which no doubt will have problems that hang the browser. Since I can’t turn off an unresponsive script in Chrome, I can’t even get to the debugger tool. Make sense?
Thanks, though.