How to detect page zoom level in all modern browsers?

Question

1. How can I detect the page zoom level in all modern browsers? While this thread tells how to do it in IE7 and IE8, I can\'t find a good cross-browser solution.

Answer 1

Your calculations are still based on a number of CSS pixels. They're just a different size on the screen now. That's the point of full page zoom.

What would you want to happen on a browser on a 192dpi device which therefore normally displayed four device pixels for each pixel in an image? At 50% zoom this device now displays one image pixel in one device pixel.