固定在顶部导航栏上不适用于Firefox，适用于其他浏览器？

Question

固定导航栏正在运行但突然停在Firefox上。当我尝试其他浏览器（chrome，即opera）时，它现在正常工作，但不适用于FF。我尝试在安全模式下启动FF，但没有区别。有什么问题？

.nav-tabs li a {
    color: #777;
}

.navbar {
    margin-bottom: 0;
    background-color: #153870;
    border: 0;
    font-size: 15px !important;
    letter-spacing: 4px;
    opacity:0.9;
}

.navbar li a, .navbar .navbar-brand {
    color: #ffef03 !important;
}

.navbar-nav li a:hover {
    color: #3AA83D !important;
}

.navbar-nav li.active a {
    color: #fff !important;
    background-color:#29292c !important;
}

.navbar-default .navbar-toggle {
    border-color: transparent;
}

.open .dropdown-toggle {
    color: #ffef03 ;
    background-color: #153870 !important;
}

.dropdown-menu li a {
    color: #ffef03 !important;
}

.dropdown-menu li a:hover {
    background-color: #153870 !important;
}

<nav id="myNB" class="navbar navbar-default navbar-fixed-top">
  <div class="container-fluid">
    <div class="navbar-header">
      <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#myNavb">
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
        <span class="icon-bar"></span>
      </button>
      <a class="navbar-brand" href="#">Obrakadabra!..</a>
    </div>
    <div class="collapse navbar-collapse" id="myNavb">
      <ul class="nav navbar-nav navbar-right">
        <li><a href="#asker">Askerleri</a></li>
        <li><a href="#hakkında">Koç Hakkında</a></li>
        <li><a href="#knededi">Ne dediler?</a></li>
        <li><a href="#onededi">O ne dedi?</a></li>
        <li class="dropdown">
          <a class="dropdown-toggle" data-toggle="dropdown" href="#">Dahası
<span class="caret"></span>
</a>
          <ul class="dropdown-menu">
            <li><a href="#mekan">Mekanı</a></li>
          </ul>
        </li>
      </ul>
    </div>
  </div>
</nav>