First: If you think the add-on doesn't work, press F1 or click the "Tree Style Tab" button that appears. The options page tells you this, but we all know people are too impatient to read the manual and expect everything to be done for them instantly.

Due to current limitations with WebExtensions (in Firefox 57.0.2), this add-on can't remove tabs from the top of the screen, so the user has to do this themselves by modifying their userChrome.css file. There is a post on the Firefox subreddit detailing how to do this, but I would like to see this guide included or referenced in the options page until such functionality can be added to the WebExtensions API: https://www.reddit.com/r/firefox/comments/736cji/how_to_hide_native_tabs_in_firefox_57_tree_style/

Caveats aside, Tree Style Tab is still an exceptional organizational tool for anyone who has a habit of opening new tabs for everything. With the tree organization, you always know which tab opened from or is related to which other tab, and the options for how you want the tabs to behave are extensive. The only faults I can find have to do with limitations of the new add-on engine, so I can't think of any reason to deduct stars. Great add-on, essential to how I navigate the web.