And I appreciate it. But it would be nice to have some built-in way to nix them. Right now I'm browsing on a MacBook Air 11" which has just 768 pixels of height. Between the menu bar, firefox UI and fixed site header, I'm left with a claustrophobic slit to view the content in.

And then I love to browse many websites by zooming in and leaning back; but once you zoom in a few steps these headers magnify to the point of absurdity.

OT, but I use Firefox and have not found that to be universally the case. But on this website, it definitely does and I really appreciate it!

That's a good point. But besides my undying love for Chrome Dev Tools, I'm kinda bugged by the idea of hacking a permanent workaround into the browser to accommodate broken sites.