FYI! - This is not true on my Mac OSX Mountain Lion computer with FF version 19. This bug was from Windows 7 machine with Firefox 20.0.
Those values depend on the zoom level even in firefox-4.0b3pre.2010-08-01-03.en-US.linux-x86_64
Core::Layout or Core::DOM Might be related: bug 435275, bug 594140.
All the values you mention are measured in CSS pixels. Zooming changes the size of a CSS pixel (not in Chrome, but in Gecko; Chrome and Gecko have very different "zooming" implementations, with quite different behavior in many cases). So when you zoom, the measured size of the screen in CSS pixels will change, since the size of a CSS pixel changed. I'm not sure what you mean by "accurate values", but you don't have them anyway in the sense that CSS pixels don't necessarily match device pixels and the brower's concept of screen.width doesn't match what the OS thinks of as the screen width in any case.