debug JS code which triggers an alert()

Question

I have a system which is built using the ext-js library. Part of the system lists orders that are flowing through an online store. When a row is clicked, additional order details are shown. A few days back, a message saying "FIXME: created panelID..." began to appear as soon as a row is clicked. After that, normal functioning continues, i.e. the error message is just annoying and doesn't break normal execution after it appears.

I am trying to debug the JS code to see under what circumstances does the error message appear, i.e. why did it suddenly start appearing. I am trying to do this with FireBug. Does anyone have any tips I could use to achieve my goal of establishing what line of code triggers the alert()? Any input on the matter is much appreciated.

Answer 1

Here's more cross-browser version of @chetan's answer

        window.alert_ = window.alert;
        window.alert = function () {
            debugger;
            alert_.apply(window, arguments);
        };