_I_
You remembered correctly, I just tested it.
Only thing is that you have click on the video that is in PiP to put it in focus, and only then can you use keyboard shortcuts to go backwards and forwards.
Firefox's PiP is probably the most feature-rich, you can also press ⌘↓ to mute the video in PiP, you can have multiple videos in PiP mode and PiP can even display captions, which is a feature no other browser I've seen has.