There are two main reasons why this issue could be occurring:

1) The plugin’s JavaScript file isn’t being included in your page.

If your WordPress theme is missing the WordPress wp_footer function from it’s footer.php file then your site isn’t able to load the JavaScript files from your plugins into the pages on your site. To check this just right click on your web page, select View Source and then look for whether the plugin’s JavaScript file is being included at the bottom of your website:

<script type='text/javascript' src='http://yourwebsite.com/wp-content/plugins/custom-facebook-feed-pro/js/cff-scripts.js'></script>

If it isn’t, then you would need to add the following line to your theme’s footer.php file, immediately before the closing body tag.

<?php wp_footer(); ?>

2) There’s a JavaScript error on your site which is stopping the plugin’s JavaScript from running.

The easiest way to check this is to go to your web browser’s Developer Tools and then select the JavaScript Console. This should list any JavaScript errors on your site in red and the source of the error. Removing any errors should allow the plugin’s JavaScript file to run correctly.