Just thought I'd add that you can do this in Chrome as well:
Ctrl + Shift + I (Developer Tools) > Sources> Event Listener Breakpoints (on the right).
You can also view all events that have already been attached by simply right clicking on the element and then browsing its properties (the panel on the right).
Right click on the upvote button to the left
Select inspect element
Collapse the styles section (section on the far right - double chevron)
Expand the event listeners option
Now you can see the events bound to the upvote
Not sure if it's quite as powerful as the firebug option, but has been enough for most of my stuff.
Another option that is a bit different but surprisingly awesome is Visual Event:
It highlights all of the elements on a page that have been bound and has popovers showing the functions that are called. Pretty nifty for a bookmark! There's a Chrome plugin as well if that's more your thing - not sure about other browsers.
AnonymousAndrew has also pointed out