You are not doing it right :) I see in the code on your website that you have some class="fa-fa fa-comments-o ..."
... That is CSS code for your own custom icons, and cannot be used with the X3 data icons, which simply use data-icon="name"
. If you click the (?) button for custom footer, you will find instructions.
Basically the format looks like this, where data-icon is a simple NAME without spaces from font-awesome. Not CSS classes.
<a href="LINK" data-icon="ICON" data-color="#AABBCC" title="HELLO"></a>
<a href="/comments/" data-icon="comments-o" data-color="#AABBCC" title="Comments"></a>
As you can see, data-icon is simply the name, identical to the names in the overview below: