title: Weird dark border :after css arrow in Firefox
body: <p>In an attempt to make an arrow in pure CSS for my tooltip, I ran across a problem in Firefox:</p>
  
  <p><img src="https://i.stack.imgur.com/JBgqg.jpg" alt="enter image description here"></p>
  
  <p>I tried to find what was causing the dark border in Firefox without success.</p>
  
  <p>Here is <a href="http://jsfiddle.net/6Wdey/" rel="nofollow noreferrer">a jsfiddle</a> and a running snippet demonstrating the problem:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.tooltip {
      position:relative;z-index:1;
      display:inline-block;padding-right:10px;
  }
  .tooltip .info {
      position:absolute;left:100%;top:-7px;
      display:block;padding:7px;border:1px solid #cccccc;
      background:#fff;
      -webkit-border-radius: 4px;
      border-radius: 4px;
      -webkit-box-shadow:  1px 1px 8px 0px rgba(0, 0, 0, .2);
      box-shadow:  1px 1px 8px 0px rgba(0, 0, 0, .2);
  }
  .tooltip .info img {float:left;}
  .tooltip:after {
      content: '';
      position:absolute;top:0;left:100%;
      display:block;
      width:0;
      height:0;
      margin-left:-13px;
      border:0 solid transparent;
      border-right-color:#cccccc;
      color:#ccc;
  }
  .tooltip .info:after {
      content: '';
      position:absolute;top:7px;left:-12px;z-index:10;
      display:block;
      width:0;
      height:0;
      border:transparent solid 6px;
      border-right-color:#fff;
      color:#ccc;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;a class="tooltip"&gt;Test for tooltip&lt;span class="info"&gt;My tootip information&lt;/span&gt;&lt;/a&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>This <a href="http://jsfiddle.net/6Wdey/1/" rel="nofollow noreferrer">second demo</a> demonstrates that background transparent is the root cause as replacing transparent by a color results in the same render in Chrome and Firefox.</p>