I really like Firefox PIP, but it's not perfect yet. I have missed the "timeline" so it would be easy to jump back if I wanted to re-watch the last bit. But I have noticed now that if the PIP window is active the arrow keys works for that which is great and it's also possible change volume with up/down arrow. So what a most miss now is that the PIP window remember its size and position from last time. Right now (on youtube) different resolutions gives different window sizes.