If you open a new windows in Nyxt browser, you'll notice that it will have the exact same tabs as the old window.
Same can be done with Emacs when in server mode: frames (windows) do share the same set of buffers.
I think this is a comfy feature, since windows' purpose is - IME - not to logically group tabs but rather only to give multi pane visualization when browsing.
So the question is: Is it possible to achieve this in Firefox?