User Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:47.0) Gecko/20100101 Firefox/47.0 Build ID: 20160623154057 Steps to reproduce: I check if fullscreen mode is available : if ( document.fullscreenEnabled || document.webkitFullscreenEnabled || document.mozFullScreenEnabled || document.msFullscreenEnabled ) { } Actual results: On version 47.0.1 of Firefox, document.fullscreenEnabled = undefined. Expected results: Since version 47, we have to use fullscreenEnabled and not mozFullScreenEnabled, but fullscreenEnabled equals undefined. I have this error in Firebug console (french message) : L’API Fullscreen préfixée est obsolète. Veuillez utiliser la version non préfixée de l’API pour le plein écran. Pour plus d’informations, consultez https://developer.mozilla.org/docs/Web/API/Fullscreen_API