I wrote a little page using Ext 4.0.7 to visualize the difference between two JSON objects to make my own life easier. It's not the cleanest code by any means, and it's a work in progress.
There are other diff tools out there that do a fine job, but I find them hard to read at a glance. The tool I wrote keeps the two objects visually separated, but allows you to identify what values changed (yellow) and what keys aren't present in the other object (green). Selecting a row highlights the corresponding row in the other object.