I just don't like to be in a browser for things that don't have to be. At least not for things I use regularly, that don't have to be. My computer has a window manager for a reason, I can move windows all over the place, and things like email I can keep always visible at work, or keep minimized and out of the way at home. But in a browser, the limited impact of tab groups aside, I'm pretty much stuck with a flat organization structure that can quickly become burdensome.

I also abhor notifications through the browser.