This feature is not on a current W3C standards track, but it is supported on the Firefox OS platform. Although implementations may change in the future and it is not supported widely across browsers, it is suitable for use in code dedicated to Firefox OS apps.
cpuSleepAllowed property determines if the device's CPU will sleep after the screen is disabled. Setting this attribute to false will prevent the device from entering the suspend state.
var isTheCPUAllowedToSleep = navigator.mozPower.cpuSleepAllowed
Return a boolean.
Not part of any specification.