Comment 118 for bug 434476

I think you want the "screen" topic, and the "locked-foreground" state to denote when to disable the screen saver.

HTMLMediaElement should already manage only disabling the screen saver when media is playing and in a foreground tab, and bug 1022669 is being worked on right now to ensure that we don't take a screen wake lock for audio-only media.

Edwin's point is that we shouldn't be taking non-screen wakelocks on desktop, they're meant for battery constrained mobile devices; for example the "cpu" wakelock code in HTMLMediaElement.cpp should really be behind b2g and android include guards.