Using deviceorientation values from Webkit browsers like MozOrientation values.

gistfile1.js

window.addEventListener('deviceorientation', updateOrient, false);
window.addEventListener("MozOrientation", updateOrient, false);

function updateOrient(e) {
  if (e.gamma && e.beta) {
    e.x = -e.gamma / (180 / Math.PI);
    e.y = -e.beta / (180 / Math.PI);
  }

  // use e.x and e.y here...
}

adapted from: https://developer.mozilla.org/en/Detecting_device_orientation#Normalizing_between_Gecko_and_WebKit