Well, I use tabs and not every website looks best at the same size. So I don't think the approach works. (FWIW, I'm also a non-full-screen user).
But you're probably on to something. I would be cool if the web browser would allow you to adjust the body size of the document without adjusting the window size.
But you're probably on to something. I would be cool if the web browser would allow you to adjust the body size of the document without adjusting the window size.