Vertical tabs make so much sense since monitors are wider than they are tall. It's better to reduce width than height
I like the desktop metaphor that computers adopted, and one way to use it is to think of different application windows as different paper documents on your meatspace desktop. You could have a rule that only 1 piece of paper is on your desktop at any time, but I find it much easier and more efficient to work with, as needed, two or more pieces of paper on my desktop. When multiple pieces of paper are on my desktop, I can arrange them such that I can easily focus on different papers by only moving my eyes, or, if the papers are relatively far apart, by moving my head and/or the rest of my body a little too.
I personally like the desk organization rule of "1 project/task per desk", i.e. you clear your desk when switching tasks to ensure only relevant things are on your desk / within your visual domain. I use computers to similar effect with different desktops/workspaces.
Tree style tabs has kept me on FF for a decade.
YMMV applies.