Really? I always maximise my browser and usually dislike not having windows full-size on my screen. It just gets fiddly otherwise. Also I like leaning back as I surf, and I need a big browser window and 120-150% page scaling for that.

Using someone else's computer with a browser that isn't fully maximised irritates me, but I generally only see that on Macs. I don't think it's very common on Windows.