 <p>Firebug displays pseudo-elements within the <a href="https://getfirebug.com/wiki/index.php/Style_Side_Panel" rel="nofollow noreferrer"><em>Style</em> side panel</a> for the selected element, not within the main HTML panel.</p> <p><img src="https://i.stack.imgur.com/TiznP.png" alt="&lt;code&gt;::before&lt;/code&gt; pseudo-element shown in *Style* side panel"></p>