''locking this thread as duplicate, please continue at [https://support.mozilla.org/en-US/questions/1076419 /questions/1076419]'' We're using a URL like "http://.....*.mp4", which will play the mp4 video files in mozilla firefox. In our code we are using <Video> element, and the video is getting played upto Firefox 37.0. After upgrading to Firefox 38.0 the video is not getting played. The error message "Media Resource could not be decoded" is displayed on debugging to the following line: document.getElementById("Video2").src="http://...*.mp4" <video id="Video2" controls/>