One website doesn't show a menu when it did before - delcore.org

One website that I have been using for a long time and was bookmarked on my menu toolbar is suddenly not showing the website menu at the top when I bring it up. I even tried removing the bookmark to bookmark it over again. However, when I go to the website to bookmark it again, the top menu doesn't appear. This is clearly a problem with Firefox because when I look up that website on another browser, the website menu at the top does show. I don't know why it won't show on Firefox. I am afraid that the problem is the result of a recent Firefox update.