If you're like me and primarily used this add-on to remove the tabs from the top, follow these instructions provided by user Soulyaris:

"Inside your profile folder(it usual c:\Users\*user*\AppData\Roaming\Mozilla\Firefox\Profiles\*something*-default (check date of modified), create a new folder named chrome. Inside the chrome folder, create two new files, userChrome.css and userContent.css. At the top of userChrome.css, add the following code:
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
/* Hides tab bar*/
#TabsToolbar { visibility: collapse; }
Save it and restart firefox. Enjoy."

Really great add-on. I'm sad to see one of its core features get changed. I hope it gets fixed.

Firefoxが57になりこのアドオンが最新版に更新された結果、ブックマークサイドバーにタブツリーが統合されてしまい、大変不便になりました。自分の使い方として左サイドバーにブックマークを表示し、右側にツリー型タブというスタイルでしたので、現状の仕様に困っています。もし、作者様にもどうにもならない仕様の更新でしたら申し訳ありません。

This extension is the only reason I still use Firefox. Something like this should be built into the browser really. Big thanks to the developer and for the effort made for it to work with the new Quantum (57) version. Required some tweaking to make it look the way I like but now works perfectly.

Make sure to visit the addon wiki for tips how to make the most of it (https://github.com/piroor/treestyletab/wiki).

I installed it because I read it could place my Tabs back to the Bottom, but it can't .
Don't know if it has any other useful features ( seems to be too Complex for a "Normal" User )

Have just started using this with FF57, as the "list tabs" drop down that I'm familiar with from v. 56 and earlier seems to have gone AWOL. Tree Style Tab addon meets this need nicely, even if a bit more cumbersome than the old button used to be.

On the plus side, it has more features that I'm guessing I will grow into: it took me a moment to find the "expand/collapse all" toggle, for example, but it's there! The themes are decent, but I would prefer one that didn't differentiate the "sidebar background" from the "tab background" -- perhaps there is one already, though. Also, it would be nice to have an option with more compressed presentation.

On the whole, though, quite a valuable addon, and kudos to the developer for having this ready to run in the new world of Firefox Quantum.

Скрываем вкладки сверху/How you can hide tabs on top
Russian:
Идем в папку профиля фаерфокса. Обычно это лежит в c:\Users\*user*\AppData\Roaming\Mozilla\Firefox\Profiles\*что-нибудь*-default (смотрите по дате измения). Заходим, создаем папку chrome, в ней сосздаем 2 файла userChrome.css и userContent.css(достаточно первого). В файле userChrome.css пишем:
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
/* Следующая строка будет прятать вкладки*/
#TabsToolbar { visibility: collapse; }
Сохраняем, идем в about:config, ставим toolkit.legacyUserProfileCustomizations.stylesheets в true, перезапускаем огнелис. Радуемся.
English
Inside your profile folder(it usual c:\Users\*user*\AppData\Roaming\Mozilla\Firefox\Profiles\*something*-default (check date of modified), create a new folder named chrome. Inside the chrome folder, create two new files, userChrome.css and userContent.css. At the top of userChrome.css, add the following code:
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
/* Hides tab bar*/
#TabsToolbar { visibility: collapse; }
Save it, check toolkit.legacyUserProfileCustomizations.stylesheets in about:config(in FF) is true, and restart firefox. Enjoy.

I'd like to try this, but can't... attempting install tells me that my FF 57 is really 48, and refuses. This is on 64-bit Debian, in case that matters.

What's with the permissions requirement?

This add-on is amazing. Instant fan.

Fantastic extension that helps me manage all the tabs I need to have open everyday. However, FireFox 57.0 update was the worst thing that could ever happen. The extension is not working as it used to and the worst, I have to deal with the traditional horizontal tabs that FireFox offers.

Come on guys, new Firefox 57 has been just released, of course the Tree-style can have some bugs, wait a little.
I'm very grateful to the author for the fast adaptation of the addon to the new FF.
Tree-style was, is and will be must-have even with some bugs.
I'm going to donate.

For those concerned about one of the most recent TST updates (I believe it's 2.2.8) that requires your permission to "Access your data for all websites", note that Piro addresses this concern in issue #1536 on TST's github project, specifically in the following comment: https://github.com/piroor/treestyletab/issues/1536#issuecomment-344792173.

I was concerned about this permission request at first, especially since I have enjoyed TST for so long and didn't want to stop using due to permission overreach. However I think I can accept the risk based on Piro's explanation of why Firefox issues the warning.

Thanks for the great add-on, Piro! I really appreciate your hard work :)

После внезапного краха всё дерево было утрачено. Теперь нужно создавать с нуля. С Tab Groups такого никогда небыло.

Must have extension! I can not work without it. However, last days, very annoying bug. New tabs are not visible in tree sometimes. They are only in standart horizontal title bar.

Can't imagine my browsing experience without this extension. Has been using it for many years. Must have, best of class!

I already use it for long time. great for my 800-900 tabs.
firefox update to 57, with no warnings...
firefox say TST is the same and took my session manager.
now all my trees become flat !!
I tried to use the migration cmd tool on the last session file, but it give access denied and also the exe can not be erase from my folder :-(
I also does not understand all the config in the advance section of this add-on.
just to mantion, it keeps new trees as created.
I could not find firefox 56 download, in order to downgrade.
how can I get all my tree structure back ?
TST 2.2.8
thanks