This is a bug, not a feature. In Youtube, I play music videos, insert them to playlist, and then later play and record the list. When playlist is played, should all songs be played from begin. But Firefox plays the songs starting at position which I last played. So, each song in the playlist are played from the middle of the songs because I typically preview the songs by listening at the middle. That is, all my music recordings from youtube may be incomplete, and that I have to record all again!!! How to "forget" the play positions from Youtube videos? I'm not going to reset hundreds of videos manually.