Find event listeners for DOM element
Webkit-/Blink-based browsers (i.e. Chrome, Safari, etc.) provide a neat utility to find out if and which event listeners are attached to a DOM node:
Firefox doesn't provide this function in its Developer Tools but has a graphical interface for events in its DOM Inspector. There's a tag labelled "event" next to each DOM node that has some event listeners attached to it. Clicking them reveals more information and allows to open the handler function in the Debugger.