在火狐和谷歌中并没有效果是怎么回事？求解

<div class="btn-group" role="group" >
             <button type="button" class="btn btn-default">1</button>
             <button type="button" class="btn btn-default">2</button>

              <div class="btn-group" role="group">
                   <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
                        Dropdown
                    <span class="caret"></span>
                    </button>
                    <ul class="dropdown-menu">
                         <li><a href="#">Dropdown link</a></li>
                         <li><a href="#">Dropdown link</a></li>
                     </ul>
              </div>
          </div>