`CustomEvent` polyfill for Firefox. Bug at https://bugzilla.mozilla.org/show_bug.cgi?id=427537

firefox-CustomEvent.js

/*global self, Document, XMLDocument, HTMLDocument, DataContainerEvent*/
!self.CustomEvent && self.DataContainerEvent &&
(function () {
"use strict";

var
	  $proto = "prototype"
	, Doc = Document[$proto]
	, XML_Doc = XMLDocument[$proto]
	, HTML_Doc = HTMLDocument[$proto]
	  // expose a CustomEvent interface alias to DataContainerEvent
	, DCE = (self.CustomEvent = DataContainerEvent)[$proto]
	, $detail = "detail"
	, $create_event = "createEvent"
	, $real_create_event = "_" + $create_event
	, get_detail = function () {
		return this.getData($detail);
	}
;

// store the real createEvent funcs as _createEvent
Doc[$real_create_event] = Doc[$create_event];
XML_Doc[$real_create_event] = XML_Doc[$create_event];
HTML_Doc[$real_create_event] = HTML_Doc[$create_event];

Doc[$create_event] =
XML_Doc[$create_event] =
HTML_Doc[$create_event] =
function (event) {
	// "CustomEvents" is explicitly unsupported; I don't agree with Mozilla's "s" leniancy
	if (event === "CustomEvent") {
		event = "DataContainerEvent";
	}
	return this[$real_create_event].call(this, event);
};

DCE.initCustomEvent = function (type, can_bubble, cancelable, detail) {
	DCE.initEvent.call(this, type, can_bubble, cancelable);
	this.setData($detail, detail);
};

if (Object.defineProperty) {
	Object.defineProperty(DCE, $detail, {
		  get: get_detail
		, enumerable: true
		, configurable: true
	});
} else if (DCE.__defineGetter__) {
	DCE.__defineGetter__($detail, get_detail);
}

}());