I've been experimenting with HTML5 video tag in javascript. I'm currently trying to develop a script that checks if a user has fully watched a video, without skipping any content. I'm doing this by interrogating the videoElement.played attribute. If the user starts the video and skips to the end, for example. The script I have developed will detect that the .played attribute is made up of dis-continuous TimeRanges. If the video is then re-played, however, the played attribute stops getting updated further. I have prepared a jsFiddle to demonstrate this: http://jsfiddle.net/rNudr/6/ Google Chrome, however, does appear to work as expected on the subsequent playback updating this attribute - so I believe this to be a bug in Firefox.