ZZZ = document.createElement('script');
ZZZ.src = '//yandex.st/dojo/1.9.1/dojo/dojo.js';
document.body.appendChild(ZZZ);
// In firebug one can use ``include`` command instead:
// include('//yandex.st/dojo/1.9.1/dojo/dojo.js');

require(["dojox/json/ref"], function(){
    window.ZZZ = dojox.json.ref.toJson(ko.toJS(objectWithCircularReferences));
});

// Then one can look for "$ref" substring in global ZZZ variable that would
// locate circular references.