The display looks great, and works great. The problem is that it refreshes the page so Firebug does not show the original request and response. You can turn on "persistence" and see the response in the Firebug history, but *NO* other plugin requires that to be done.
Also Firebug will recognise JSON even if the delivered content-type is wrong, while this plugin does not. That may be considered a design feature, but I think it needs an override or option so I can tell it, "yes, this IS JSON, even if the server doesn't say so".
If that one drawback can be resolved, then it gets full marks.