I have a quad monitor setup, 4x 42" 4k monitors. I also use AltSnap and FancyZone

This functionality was already available with addon Tiletabs WE https://addons.mozilla.org/en-US/firefox/addon/tile-tabs-we/

But even with all this, there is no way to snap multiple views together reliably. And actual split window, in the specific cases that it's needed, is useful. It's just not a thing a regular old normie would need.