When I close a tab that had a video playing, the picture-in-picture box will stay there after I close the tab. The picture is just a white box. The controls are there, but when I click on any button, nothing happens. I can only move the box around and resize it. It usually happens when I close the tab while the video is playing, but sometimes it happens when I close the tab and the video is paused. It happens on videos that were in a picture-in-picture box and videos that weren't. I go into setting and disable picture-in-picture which will stop new picture-in-picture boxes, but won't get rid of the white box. The only way to get rid of the white box is to close FireFox completely and then reopen it.