Add this to a snippet and include that snippet before the </body> tag. Adds an edit link to edit content. Only shows up if you are logged-in your store's admin.

new_gist_file.liquid

{{ '//maxcdn.bootstrapcdn.com/font-awesome/4.1.0/css/font-awesome.min.css' | stylesheet_tag }} 
<style>
.edit-tool {
  float: right;
  position: fixed;
  right: 0;
  top: 70px;
  background-color: white;
  padding: 5px 10px;
  -webkit-box-shadow: -1px 0px 3px 0px rgba(50, 50, 50, 0.6);
  -moz-box-shadow:    -1px 0px 3px 0px rgba(50, 50, 50, 0.6);
  box-shadow:         -1px 0px 3px 0px rgba(50, 50, 50, 0.6);
}
.edit-tool a {
  color: #555;
  cursor: pointer;
}
</style>
<script>
$(window).load(function() {
  if ( $('#admin_bar_iframe').size() ) {
    $('body').append('<div class="edit-tool"><a><i class="fa fa-pencil-square-o"></i> Edit this </a></div>').find('.edit-tool a').click(function(e) {
      e.preventDefault();
      (function(e,a,g,h,f,c,b,d){if(!(f=e.jQuery)||g>f.fn.jquery||h(f)){c=a.createElement("script");c.type="text/javascript";c.src="http://ajax.googleapis.com/ajax/libs/jquery/"+g+"/jquery.min.js";c.onload=c.onreadystatechange=function(){if(!b&&(!(d=this.readyState)||d=="loaded"||d=="complete")){h((f=e.jQuery).noConflict(1),b=1);f(c).remove()}};a.documentElement.childNodes[0].appendChild(c)}})(window,document,"1.10.1",function($,L){var s=$(location).attr("hostname"),u=$(location).attr("href")+".json";$.ajax({url:u,type:"GET",dataType:"json",success:function(o){if(o.hasOwnProperty("product")){var t=o.product.id;window.location.href="https://"+s+"/admin/products/"+t}else if(o.hasOwnProperty("collection")){var t=o.collection.id;window.location.href="https://"+s+"/admin/collections/"+t}else if(o.hasOwnProperty("page")){var t=o.page.id;window.location.href="https://"+s+"/admin/pages/"+t}else alert("Sorry, but you cannot use this here.")},error:function(){alert("This cannot be used here.")}});});  
    });
  }
});
</script>

It no longer works on Article pages, now that the URL system has been changed.