Turns out this was an artefact of a Firebug bug. The Ajax request was cancelled, but Firebug continued reporting it as active. Details here.
I have long runnin
Another great article on handling this is found here: http://www.bennadel.com/blog/1500-Catching-Timeout-Errors-With-jQuery-Powered-AJAX.htm.
I simply converted my .getJSON request to .ajax and added the timeout/error handling.
Thanks!