Comment by lproven

But it causes cognitive overhead: you need to think about which bits of the title-cum-button bar are safe to grab, as opposed to which overloaded and do other things, which are possibly useful.

I use Firefox. I also use macOS a lot. Firefox assumes your tabs are horizontal. Mine are not (using a built in feature).

So it doesn't use the title bar much. So there's an option to turn it off. It's off by default. Result, the actual top bar is a cluttered toolbar and it's hard to move the Firefox window.