Click your window's green (zoom) button.

It will actually maximize Safari (or Chrome) now.

Like in this picture. But don't click this picture. It's just a picture.

Unlike Firefox, Safari and Chrome follow OS X standards, which means the green button makes the window the minimum size that fits the page's content. This page has a giant div in it, so the green button will now enlarge the page to maximum size.

Lovingly stolen from maximizechrome.com when it went down.