Client side Add-on for preloading images and music into the browser. Preloaders for preloading images and music into the browser to improve the user experience. You only need to add a listener to the preloader and it callback when an image/audio has been loaded. Both preloaders can be given multiple things to load at one time. With music the loader tries to figure out the audio formats that the browser can handle (probably/maybe) in order: .ogg, .mp3, .wav (having all 3 formats available is recommeded) If nothing is supported then the preloader will stop and fire a failed event.