Code snippet to disable the WP Featherlight plugin on singular posts.

disable-wp-featherlight-singular-posts.php

add_action( 'wp_enqueue_scripts', 'sitecare_disable_featherlight_singular_posts' );
/**
 * Disable WP Featherlight on singular post entries.
 *
 * @author WP Site Care <http://www.wpsitecare.com/>
 * @access public
 * @return void
 */
function sitecare_disable_featherlight_singular_posts() {
	if ( is_singular( 'post' ) ) {
		add_filter( 'wp_featherlight_load_css', '__return_false' );
		add_filter( 'wp_featherlight_load_js',  '__return_false' );
	}
}