Is there a way to determine the string and file name from which XHR was released by Firebug or Web Inspector (possibly Opera Dragonfly / IE Developers Toolbar)? If this does not happen, then what is the way to find it? Just looking up the code for the called URI? (often it will be built though)
In Developer Tools (chrome), you can set breakpoints for any XHR from the Script tab.
Firebug http://getfirebug.com/doc/breakpoints/demo.html