Like, you have one browser window, which has multiple subwindows within it, each of which is another browser?
@foone Opera, back when it was *actually* Opera, with the Presto engine and owned by Opera Software of Norway, not yet another Chrome wearing the skin of a purchased name.
It did it with a tab bar as a window switcher, so was the best of both worlds.
The screenshot in https://www.lionsphil.co.uk/phd/ is three arranged subwindows. Unfortunately I cropped away the outer UI.
"Split view", pah.
@foone Opera (real Opera, not Chromium wearing an Opera trenchcoat) was MDI, except on Mac OS
when they added “tabbed browsing”, it was basically implemented as a taskbar