I had to debug an issue this morning where an Ajax call ($.getJSON) failed in every browser except Firefox.
Some googling lead to this answer on Stackoverflow which describes how to setup error handling for ALL Ajax calls in your code.
Like most things with jQuery, it's very simple:
$(document).ready( function() { $.ajaxSetup( { 'error': function(XMLHttpRequest, textStatus, errorThrown) { alert('Ajax Error: (' + textStatus + ') ' + errorThrown); } }););
If you read that answer, you'll notice he suggests malformed JSON as the most likely culprit for the callback to $.getJSON not firing.
I added the above error handler and, sure enough, it was a bad-JSON error. I ran my JSON through JSONLint to discover an error that I've run into many times and will, hopefully, someday, remember to look for.
[ {"ant":"bear"}, {"cat":"dog"}, ]
See that comma after "dog"}? Firefox is pretty forgiving about that sort of thing but Internet Explorer (and Chrome) don't like it. I'm constantly forgetting about removing that trailing comma, I suspect because that's perfectly valid when declaring arrays and dictionaries in Python.