How can I check if browser tab is active and visible?

I am making website with contests and I want to check, if user's tab in browser is active and visible. For example, if person hides browser window or switches tab with my website, the tab won't be active and I need to know it. Can i do this or something like this?

I know about Firefox visibility API, but it checks only visibility. So, if there are two windows on the screen and one of them is browser window with website, website is visible. But other window can be active and my website will be visible, but not active. It It isn't something that I want