[pcwalton]

> In instances where CSS doesn't affect the styling of the control, the browser can use native controls. As far as I know, every browser _except_ Firefox does this.

This is not true. It's not just the styling of the control itself that makes it infeasible to just stick an NSButton inside the browser's NSView; it's about the way a control interacts with everything else on the page.

Source: I work on browser graphics.