The Idle API is used to notify an app when the user is idle. This lets an app take action when the user is doing nothing with his device. The most common use case is to save battery power; in this case, it is commonly used in conjuction with the Power Management API.
readyState should be used sparingly; L10n.ready() and L10n.once() are usually better suited for controlling when code is run relative to the state of the localization.
The navigator.mozAudioChannelManager object provides access to the mozAudioChannelManager interface, which is used to manage your Firefox OS device's audio channels, including setting what channel's volume to affect when the volume buttons are pressed inside a particular app.