pipn: auto picture in picture автор gavink

!Important this addon will not work unless you have Firefox labs Picture-in-Picture: auto-open on tab switch enabled or in about:config picture in picture enable when switching tabs to true.
media.videocontrols.picture-in-picture.enable-when-switching-tabs.enabled = true

Usage:
Any time you leave firefox with audio or video playing it will automatically open a new tab to enable picture in picture mode, and when you reenter firefox it will close the newly created tab.