When you turn on Firebug, there the tab is called "Network" - all requests are displayed, especially ajax. The Network tab allows you to filter requests and check request / response headers, status code and message.
So, if you turn on Firebug and open the "Network" tab (you may need to enable tracking first, in this case it will display a message), you will see if there was a request where you expected it to be.
To see only ajax requests, check the XHR in the top bar, just below the common tabs.
source share