The behavior is strange why it won't open the link, I can even right click and choose to open in a new tab. The solution I came up with is to use JavaScript inline to force the event. Here's the code for twitter you can apply the same to the Facebook tag: Here the twitter link works in this updated JS FIDDLE
<li style="display:inline; margin-right:10px;"><a href='http://twitter.com'
onclick='window.open("http://twitter.com");return false;'><i class="fa fa-twitter fa-2x">
</i></a></li>