Best extension hands down.

works well, and, is simiarly to the screenshots. If you like side tabs, this is a great add on.

This is an excellent, free tool. It's super handy for keeping my tabs organized. It has the occasional glitch, but I seem to be able to clear them by pressing F1 twice (to close the Tree Style Tab pane and reopen it).

This plugin was one of the reasons why I moved back to use Firefox. This feature should be default in all the browsers.

@Alexandru Nedelcu -- Any way to restore the window control buttons (e.g., min, max, close)?

TST is a great addon, but the need to continually write your own CSS code to make it behave within reasonable expectations is frustrating. Moreso, the changing css code makes this work-around unreliable; see above. The latest change to FF has rendered the previous solutions obsolete: eliminating the duplicate horizontal tabs using the previous method also eliminates the window controls.

The horizontal tab bar can be hidden via userChrome.css, see: https://gist.github.com/alexandru/0f8b9a845342dd919d48dccc844a7135

This is the addon that keeps me locked to Firefox - I simply can't move to a browser without vertical tabs. Thank you, Piro.

best extension

This great addon is the main reason why I'm using Firefox.