function testProps( props, prefixed ) {
        for ( var i in props ) {
            if ( mStyle[ props[i] ] !== undefined ) {
                return prefixed == 'pfx' ? props[i] : true;
            }
        }
        return false;
    }
testProps is a generic CSS / DOM property test; if a browser supports
  a certain property, it won't return undefined for it.
  A supported CSS property returns empty string when its not yet set.