Firefox introduces Split View: Two tabs side by side, right where you need them

https://blog.mozilla.org/en/firefox/split-view/

Split View in Firefox: Two tabs side by side, right where you need them | The Mozilla Blog

Much of what we do on the web involves looking at more than one thing at a time – booking tickets while checking your calendar, taking notes as you go th

What makes this better than having two full browser windows side by side?
If you want to switch back and forth between "these two web things side-by-side" and "something else" over and over, then in that case it's better than two full browser windows side-by-side because they come into the foreground and vice versa as a unit.