<p>How to add some content to all posts? Easy, install this plugin to your website/blog. When activated, a new option in the Posts menu will be able, Add To Post Footer option. Click there and insert the content what you want to add to all posts footer. Save it and it’s done. As you activate the plugin, all posts will have the content. If you don’t want more the content, just deactivate the plugin.</p>


Add To Post Footer

Add some content to the bottom of all your posts. You can add images and HTML too. Install and activate it, it's easy!

Anand Kumar

Digital Liberation

<p>If you are running a WordPress site then sooner or later you need to insert some kind of code to your website. It is most likley a web analytics code like Google Analytics or may be social media script or some CSS stylesheet or may be Custom fonts. This plugin will do all the magic. Even if you want to insert those codes in a custom post type.</p>
<p>All you have to do is adding appropriate html code.</p>
<p>Don’t forget to wrap your code with proper tags.</p>
<pre><code><script type="text/javascript">
YOUR JS CODE HERE
</script>
</code></pre>
<p>Or for CSS:</p>
<pre><code><style type="text/css">
YOUR CSS CODE HERE
</style>
</code></pre>
<h4>Why use this plugin:</h4>
<ul>
<li>To insert CSS and JavaScript codes to <code><head></code> or before <code></body></code>.</li>
<li>To insert code to <code><head></code> of any single page or post.</li>
<li>To insert code to Custom Post Type [New Feature].</li>
</ul>
<p>The plugin should be compatible with WooCommerce.</p>
<h4>What it does not offer</h4>
<ul>
<li>You can’t insert/execute PHP codes.</li>
</ul>
<p>Almost all WordPress theme do support this “Header and Footer Scripts” plugin. If the codes are not appearing in your site [ask for support] or look at your theme file if they have standard <code>wp_head</code> and <code>wp_footer</code> hooks.</p>
<h4>Important Links</h4>
<p>For furhter information you are welcomed to follow these links:</p>
<ul>
<li><strong><a href="https://github.com/anandkumar/header-and-footer-scripts/wiki" rel="nofollow ugc">Read Documentation</a></strong></li>
<li><strong><a href="https://wordpress.org/support/plugin/header-and-footer-scripts/" rel="ugc">Get Support</a></strong></li>
<li><strong><a href="https://github.com/anandkumar/header-and-footer-scripts" rel="nofollow ugc">GitHub Repository</a></strong></li>
</ul>


Header and Footer Scripts

good

Como es posible que al desinstalar el plugin, si no has borrado el script te deje el código ahi metido. Y luego a averiguar de donde vienen los errores. 

Al desinstalar te deja el código

Header and Footer Scripts plugin allows you to add scripts to WordPress site's  and just before closing  tag.

Add To Post Footer vs Header and Footer Scripts