glyphicon-lock未显示

Question

我正在使用ASP.NET MVC Web应用程序，我正在使用Bootstrap 3.

我在登录视图中有以下标记来显示用户名和密码：

<fieldset>
  <div class="input-group input-group-lg">
    <span class="input-group-addon">
      <i class="glyphicon glyphicon-user blue"></i>
    </span>
    <input type="text" class="form-control" placeholder="Username" name="Username" value="@Model.UserName">
  </div>
  <div class="clearfix"></div><br>

  <div class="input-group input-group-lg">
    <span class="input-group-addon">
      <i class="glyphicon glyphicon-lock blue"></i>
    </span>
    <input type="password" class="form-control" placeholder="Password" name="password">
  </div>
  <div class="clearfix"></div>

  <p class="center col-md-5">
    <button type="submit" class="btn btn-primary">Login</button>
  </p>
</fieldset>

但是，密码字段中的glyphicon-lock未在IE，FF或Safari上显示：