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:
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.