Could someone explain what's going on with this comment and why its upvoted so much? It's a genuine question. What's wrong with his phone (and how do you know what he uses)?
Not any PiP window, only ones that use the protocol. Firefox should use it. Though I'd be surprised if there wasn't some Kwin extension to automatically make the PiP windows always on top like the extension you mentioned or the Gnome "PiP on top" extension
Plasma lets you pin any window to be always on top (short of fullscreen apps), and you can set up rules to automatically set that behavior for any pip window.
Damn, I really would like to pip the stremio app and not use the web version when using plasma, its a very convenient extension to have in gnome and keeps me there