If the buttons are small, they are harder to click. It's also harder to understand what they do, which is important when they have icons that are just cryptic monochrome squiggles.

What's the merit in making the buttons unobtrusive? What are you going to do with all those saved pixels? There is no pixel shortage on desktop! That's a mobile design consideration.

When the browser is covering a sixth of my screen it's already uncomfortably large. There is no reason to save hundreds of pixels when there are literally millions to spare.