Bootstrap 3折叠导航菜单无法在移动设备上运行

Question

我正在bootstrap 3内建一个网站Ecovalley Holidays。但我的collapsed toggle menu无效mobile devices，而是显示与大型显示器相同的导航菜单！此外，切换菜单正在Firefox (Ctrl+Shift+m, responsive design view )上运行。我的导航类似于以下代码：

<nav class="navbar" role="navigation">
    <div class="container">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#topnav">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <?php echo $this->Html->link('Ecovalley', array('controller' => 'pages', 'action' => 'home'), array('class' => 'navbar-brand')); ?>
        </div>
        <!-- Collect the nav links, forms, and other content for toggling -->
        <div class="collapse navbar-collapse" id="topnav">
            <ul class="nav navbar-nav navbar-right">