下記のスニペットでFirefox 49を使用すると、あなたが上に貼り付けたコードは、マイナーなHTML解析の微調整で完璧に動作しました。
<html data-ember-extension="1" class="fa-events-icons-ready" lang="en"><head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- The above 3 meta tags *must* come first in the head; any other head content must come *after* these tags -->
<title>Bootstrap 101 Template</title>
<!-- Bootstrap -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
<!-- HTML5 shim and Respond.js for IE8 support of HTML5 elements and media queries -->
<!-- WARNING: Respond.js doesn't work if you view the page via file:// -->
<!--[if lt IE 9]>
<script src="https://oss.maxcdn.com/html5shiv/3.7.3/html5shiv.min.js"></script>
<script src="https://oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
<![endif]-->
<link href="https://use.fontawesome.com/b703330c8c.css" media="all" rel="stylesheet"></head>
<body>
<style>
.collapsibleList li>input+* {
display: none
}
.collapsibleList li>input:checked+* {
display: block
}
.collapsibleList li>input {
display: none
}
.collapsibleList li list-group-item>.badge {
float: right
}
.collapsibleList label {
position: relative;
display: block;
padding: 10px 15px;
margin-bottom: 0px;
background-color: #fff;
border: 1px solid #ddd;
cursor: pointer
}
</style>
<h1>Hello, world!</h1>
<ul class="collapsibleList">
<li><label class="list-group-item" for="mylist-node6">Highest Win Ratio<span class="badge">Click Me!</span></label>
<input id="mylist-node6" type="checkbox">
<ul>
<li class="list-group-item">
<img src="avatar”"> #1 <a href=""> Name</a> <span class="badge">61.76% </span>
</li>
<li class="list-group-item">
<img src="avatar"> #2 <a href=""> Name</a> <span class="badge">50.75% </span>
</li>
<li class="list-group-item">
<img src="avatar"> #3 <a href=" "> Name</a> <span class="badge"> 44.59%</span>
</li>
</ul>
</li>
<li class="list-group-item ">
<a href=""><i class="fa fa-gamepad"></i> ClassicHG Leaderboards</a>
</li>
</ul>
<!-- jQuery (necessary for Bootstrap's JavaScript plugins) -->
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<!-- Include all compiled plugins (below), or include individual files as needed -->
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>
<script src="https://use.fontawesome.com/b703330c8c.js"></script>
</body></html>
