Programmatically stop Javascript execution in FireFox/FireBug

I am currently debugging complex Javascript/AJAX code written with mootools with FireBug. I am looking for a way to stop the JS execution as if it was a breakpoint programmatically.

Is there a way to tell which javascript file holds an event handler?

This problem has bothered me for a while and Im sure theres some sort of technicality which stops this from being possible, but is there a way to find which Javascript file is linked to a button?