Allow autoplay of media with sound
Firefox may be blocking media with sound from playing automatically. To allow media autoplay, see Allow or block media autoplay in Firefox.
HTML5 audio and video
Firefox has built in support for open media formats usually associated with MP3, WebM, Ogg and Wave containers. However, MP4 containers usually depend on platform decoders for AAC and H.264 audio and video streams. For more information, see Fix video and audio playback problems on Firefox for Windows and HTML5 audio and video in Firefox.