处理FF的domReady bug

   // fix document.readyState for Firefox < 3.6
    var d = document    
    if ( typeof d.readyState !== 'string' && top.netscape ) {
        d.readyState = 'loading';
        d.addEventListener('DOMContentLoaded', function() { 
            d.readyState = 'interactive'; 
        }, true);
        addEventListener('load', function() { 
            d.readyState = 'complete'; 
        }, true);
    }