From Firefox 33 you'll see an "ev" icon in HTML Pane, next to elements that have event listeners bound to them:
Click the icon, then you'll see a popup listing all the event listeners bound to this element:
Each line contains:
- a pause button: click that to go to the event listener in the Debugger, where you'll be able to set a breakpoint in it
- the name of the event
- the name and line number for the listener: click this to see the listener function in the popup
- a label indicating whether the event bubbles
- a label indicating the system that defines the event. Firefox can display:
- standard DOM events
- jQuery events
- React events (new in Firefox 53)