HUGE thanks to previous reviewer GeBra for revealing this. In Firefox 57+, you can simply go to about:config and set browser.tabs.loadBookmarksInTabs to true. You can do this by simply double-clicking the setting. In other words, this functionality is 100% available in Firefox 57 and above; this add-on may not work, but it is not necessary either. I am very relieved, as this was a really great feature. It just seems to improve the "flow" of browsing so much to have bookmarks open in a new tab automatically. Thanks so much for this add-on, it was really great when it was necessary and for all we know it may have inspired Mozilla to implement the feature officially.