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
Looks like default-off (phew), unlike Chrome. A feature no-one asked for. Especially in FF where memory is well managed.