How to customize/add extension to post URL/permalink?

I’ve successfully moved our blog from Wordpress to Ghost. The only thing left is to add facebook comments but the post URLs are different in Ghost, resulting in the Facebook comment integration not loading previous comments. Our post URLs from Wordpress ends with “{slug}.html”, in Ghost it ends with “/{slug}/”. I’ve already tried changing the routes.yaml file but it requires the permalink to end with “/”.

In summary, Facebook comments won’t load because the URL is different. What can I do to fix this?