Mayo Moriyama

<p>This is a plugin insert any HTML tag you like into footer area in whole website.</p>
<p>このプラグインは、何でもあなたのすきなHTMLタグを、サイト全体のページ末尾に表示させることができます。</p>
<h3>English</h3>
<ol>
<li>Upload <code>navicast.php</code> to the <code>/wp-content/plugins/</code> directory.</li>
<li>Activate the plugin through the <code>Plugins</code> menu in WordPress.</li>
<li>Set your text through the <code>Option</code>><code>Reading</code> menu in WordPress.</li>
</ol>
<h3>日本語</h3>
<ol>
<li><code>navicast.php</code>を<code>/wp-content/plugins/</code>ディレクトリにアップロードします。</li>
<li>管理画面上の<code>プラグイン</code>から、プラグインを有効にします。</li>
<li>管理画面上の<code>設定</code>><code>表示設定</code>から、表示させるHTMLタグを設定し、保存します。</li>
</ol>


Mayuko Footer Tag Manager

This is a plugin insert any HTML tag you like into footer area in whole website.

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.

Mayuko Footer Tag Manager vs Header and Footer Scripts