listen for focus/blur on nsiWindowWatcher or nsiWindowMediator? for firefox extension

Question

I would like to find out whether or not the main browser window is focused. Is this possible to achieve using nsiWindowWatcher or nsiWindowMediator? Been trying to digging Mozilla's documentation with no luck so far..

Firefox addon/jetpack is not an option though

Answer 1

never mind turns out addEventListener('focus'/'blur') on the main js file works fine