这是Firefox 4的二进制搜索，因为我不知道它公开的任何变量：
<style id=binarysearch></style><div id=dummyElement>Dummy element to test media queries.</div><script>var mediaQueryMatches = function(property, r) { var style = document.getElementById('binarysearch'); var dummyElement = document.getElementById('dummyElement'); style.sheet.insertRule('@media (' + property + ':' + r + ') {#dummyElement ' + '{text-decoration: underline} }', 0); var matched = getComputedStyle(dummyElement, null).textDecoration == 'underline'; style.sheet.deleteRule(0); return matched;};var mediaQueryBinarySearch = function( property, unit, a, b, maxIter, epsilon) { var mid = (a + b)/2; if (maxIter == 0 || b - a < epsilon) return mid; if (mediaQueryMatches(property, mid + unit)) { return mediaQueryBinarySearch( property, unit, mid, b, maxIter-1, epsilon); } else { return mediaQueryBinarySearch( property, unit, a, mid, maxIter-1, epsilon); }};var mozDevicePixelRatio = mediaQueryBinarySearch( 'min--moz-device-pixel-ratio', '', a, b, maxIter, epsilon);var ff35DevicePixelRatio = screen.width / mediaQueryBinarySearch( 'min-device-width', 'px', 0, 6000, 25, .0001);</script>
