Firefox versions greater than 71 now have the ability of Picture in Picture.
However the small blue rectangle that slides out when you hover over it
is centred on the middle of the right hand edge of the video play back
window. This is exactly where the right hand play next video white arrow >
is situated as well. When you wish to play the next video it picks up Firefox new Picture in Picture instead of the next video arrow >.

NOTE: I have also posted this in Mozilla Support Forum
However the small blue rectangle that slides out when you hover over it
is centred on the middle of the right hand edge of the video play back
window. This is exactly where the right hand play next video white arrow >
is situated as well. When you wish to play the next video it picks up Firefox new Picture in Picture instead of the next video arrow >.

NOTE: I have also posted this in Mozilla Support Forum

