Note for Future Dan: if you want Firefox’s picture-in-picture (popout video) mode to be available for videos of less than 45 seconds, the setting you need is
media.videocontrols.picture-in-picture.video-toggle.min-video-secs. This is useful if you’ve got a playlist of multiple short clips
(which reuse the same
<video> element) that you want to treat as a single long video for the purpose of picture-in-picture.