[j1elo]

Why does the Window Manager have to provide focus and even visibility info to the application? I could foresee an evolution of runtime controls where "Is Focused" is a user-selectable permission for apps, just like how the browser requires user approval to allow web notifications or PeerConnection access to network or webcams.

[iroddis]

I think this case was the browser was active, but not the tab, so the browser reports that.

Many, many telemetry metrics have been added in the name of power and efficiency. If a page refreshes every 30 seconds, is it still worthwhile doing it when the tab isn’t active? It would be better to wait until the tab is active again, then refresh immediately.

That being said, all of these capabilities are a privacy nightmare, only increasing the precision of browser fingerprinting and user monitoring. Firefox could have taken a stance on refusing to implement them, but I don’t think it has an easy opt out.

[pseudalopex]

Disable Page Visibility extension is available for Chrome and Firefox. And StopTheMadness for macOS Safari.

[redox99]

Because it's pretty useful, for example to avoid refreshing data if the tab is unfocused and refresh immediately on focus.