This addon does exactly what it says it does. It open links in new tabs. Not bookmarks - there's a preference for that (set browser.tabs.loadBookmarksInTabs to true; you may need to create it as a new Boolean setting if it doesn't already exist). Not searches - there's a preference for that too (browser.search.openintab - also set it to true). Just links.

Like many others I do wish it would open addresses typed into the address bar in a new tab, and it would be wonderful of the developer could do that, but it's unfair to give him a low rating for not doing something the addon is neither designed no claimed to do. So, I give it five stars, because it is working exactly as it's supposed to for me in Firefox 57.