Firebug - Check DOM Event Bindings

Go to Firebug Console edito and run this command

$('#mybutton').events('data')

See in the console logger  It will show the events bound with the mybutton element just like

object {click=}

You can further click on that link to see the Handler Node, Note that hovering the mouse over the word function(written next to Handler) will show a tooltip telling file name and line number. Click the word function to go to the line of code in script tab.