Currently, Firefox supports opening a video in Picture-in-Picture mode with the shortcut Ctrl + Shift + ]. However, this only works for one video at a time — the currently focused one.
For heavy users of YouTube, Twitch, and other video platforms, it would be extremely useful to have a shortcut that opens all currently playing videos into PiP windows at once.
For example, a suggested shortcut could be:
Ctrl + Shift + Alt + ]
This would make Firefox much more powerful for multitasking, especially when watching multiple livestreams or monitoring several videos simultaneously.