Make compatible with Firefox 3.6

* getComputedStyle needs second argument, set to null as per default value - https://developer.mozilla.org/en/docs/Web/API/window.getComputedStyle
* addEventListener needs third argument (useCapture), set to false as per default value - https://developer.mozilla.org/en-US/docs/Web/API/EventTarget.addEventListener
Version 2.0.3