It's a must have! Thanks.

It's just the Firefox 57 upgrade that is a bit hard but it is not the developer's fault! I was just surprised not to see my vertical tabs on the left (even after some FF restarts) until I read that there is a button to display it! Maybe there is a bug or the developer simply forgot to make this visible by default or maybe FF57 does not allow this.

For the upgrade, I had to follow the migration tutorial here: https://github.com/piroor/treestyletab/wiki/How-to-convert-session-information-from-old-TST-0.19.x-to-new-TST-2.x
And then I used the following CSS rule to hide the "standard tab bar on the top": https://github.com/piroor/treestyletab/wiki/Code-snippets-for-custom-style-rules#hide-horizontal-tabs-at-the-top-of-the-window-1349
First I had to created a folder chrome inside my user profile directory, then a new file userChrome.css where I placed the following code:
#TabsToolbar {
visibility: collapse !important;
}
This hides the "standard tab bar on the top" as expected.
Now I finally have TST quite as before, and at least as usefull as before!

Thanks again @Piro and other developers to keep maintaining this add-on!

works great with WebExtensions!

It works great with firefox 57. Almost like in 56 but need to configure it a little bit. Use github instructions to get TreeStyleTab which it was at firefox 56.

На firefox 57 работает практически также как и на 56 с небольшими допилами. Используйте инструкцию на гитхаб чтобы сделать всё как ранеьш.

JHP - Many thanks for referencing the code to remove the horizontal tabs. Can you tell me the name of the 'user profile directory' folder, as I can't find it in Windows Explorer.

There is just nothing else like it. Nesting tabs allows you to have many many tabs open while staying organized. This is excellent for research as you can nest result pages of a google search under the google page - which also provides a conveniently named header. The drag-and-drop interface is intuitive and responsive. It is also reasonably customizable. I would be seriously sad if this extension were to go away.

I love tree style tab. Tree Style Tab has brought order out of chaos for me. The whole internet experience is much more organized and enjoyable with it.

In the latest version for Firefox Quantum there is an icon to show/hide the side panel. Before I sometimes had problems with the tree panel not rendering completely and I couldn't see the show/hide bar to hide it, that problem is all gone now.

One thing I don't like about the latest version is that the standard tabs are now at the top and not hidden when the side panel is visible. Sometimes when trying to move the window I accidentally click on one of those tabs.

Another issue is that the side panel has a header at the top. I assume that header will be useful for someone who has more than one side panel installed, but for me right now it is not useful.

MUST HAVE & BEST addon even with 360 tabs grouped on the left side. Good performance even with 5GB RAM used for DNA & engineering on 64 bit FF ESR. I will stay on ESR 52 (32 and 64 bit FF) until this addon is properly and fully supported by FF and addon creator. If I have to I will stay with ESR 52 even when it is no longer supported in 2018. And I don't care if TST has some bugs; they're mostly minor and mostly affect the special case of 1 tab or 1 group of tabs. Work-around is to just have 2 tabs opened or more and it's perfect. I would pay $$$ to Piro for his great work !! Prior to using ESR I was fed-up with many addons and icons breaking with every FF update. I dreaded the updates but there's the security issues. I was spending way too much time repairing FF (non-ESR). Intel i7 and 16 GB RAM underused. They should have kept the older addons in a sandboxed/container within a 1 single thread. And add the newer web-extensions in their new multi-thread machine to avoid killing decades of software by hardworking dedicated addon developers. So much addon software destroyed in 1 swoop :( And I have over 50 addons. Even with the very hungry NoScript and other necessary privacy and security addons.

E' così comodo in verticale tutti i tab

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.

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).

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.

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.