I\'m using window.innerHeight and window.innerWidth instructions to get the browser\'s available window size. It\'s working with firefox, safari (on a mac
Check Apple's documentation on how to set the viewport for Mobile Safari, and how it scales: http://developer.apple.com/library/safari/#documentation/appleapplications/reference/safariwebcontent/UsingtheViewport/UsingtheViewport.html
Basically, you can set a scale for the viewport, and make it default to whatever you want by setting a meta tag on your HTML page.