Vertical tabs. I have a plugin on Firefox that lists tabs vertically and they’re also stacked so tabs opened in a tab get nested in that tab. I can’t remember the name, but I’ll update this comment with it when at my computer if anyone wants it.
Tree style tabs! Best used with css changes to remove the horizontal tab bar and the side menu header
Given that monitors tend to be wider than they are high, can’t see how this is a win tbh. Unless you’re going vertical monitor, then it’s the same real estate right?
E: words E2: I reread, if you can find that add-on I’d love to know what it is.
I thought the same when I first heard about it, but I gave it a go anyway. It’s a game changer.
Tree style tabs: https://addons.mozilla.org/en-US/firefox/addon/tree-style-tab/