Suppress content access to page visibility API
The document.visibility
property and the visibilitychange
event let content know if the user has selected or deselected a tab. If the user switches from tab A to tab B, then tab A can receive a "hidden" event at the same time that tab B receives a "visible" event. So it seems potentially useful to suppress this information.
See https://developer.mozilla.org/en-US/docs/Web/API/Page_Visibility_API