Thread:Extension talk:LiquidThreads/Redesign/Page Updates and Refreshes/reply (9)

The DOM actually has a little bit of information available on if the page is focused on. ie: It's possible to tell the difference between when the user has the tab open in front of them, and when it's an inactive tab, or iirc even if the browser isn't right up at the front. That's another good way to check if any update polling should be done.