It may look strange, but there is no need to panic, there is no security issue in your site, and this won't cause any harm to your page, in fact, it never access your site.
For that reason, it is called Ghost Spam and can show up in different parts of your reports. Usually, the purpose of this type spam is to promote some page or drive traffic to a website, to sell SEO services or to redirect you to an affiliate page. In this case is to promote a search shell addon for Firefox.
With thanks to www.ohow.com for this article.