User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:51.0) Gecko/20100101 Firefox/51.0 Build ID: 20170125094131 Steps to reproduce: Firefox v52 (but already noticed within v51). Device: Samsung Galaxy A5 (2015) Android 6.x I used google search to find any youtube video. Select link to open youtube video by webinterface (no youtube app installed on my device). Tab on video area to get submenu. Increase video size to full screen. Use Back button to get back to list of videos (still inside youtube). Select any link to get to another video. Try to enlarge this video to fullscreen -> not possible. Actual results: Subemnu somehow freezes. Timebar stops at current position, but video and audio remains playing. Video remains in small size. The only chance to solve this situation is to close Firefox and restart it. On my device, very easy to reproduce. Expected results: Whenever I select any youtube video by webinterface, I should be able to enlarge the video to fullscreen. Note: I noticed that there are similar issues already in bug database. However, all these issues are already solved - so I raised new ticket.