Following the message of XenGeek
I used this code to remove Tabs keeping the title bar.

/* Remove horizontal tabs */
#tabbrowser-tabs {
visibility: hidden;
margin-top: 40px;
margin-bottom: -50px;
}

/* Remove sidebar header */
#sidebar-header {
visibility: collapse;
}

Anyway this add-on is very good, I don't understand why this tree tab menu is not a standard in Firefox. Saved me a lot of time and energy !

Thanks a lot !

Extension is very handy. But last update asks for accessing all my web data. Why??? I'm not installing it for now cause there is no justification anywhere why this permission has been requested.

To add on to Anonymous user fc7bf5's comment. If you want to get rid of the Horizontal Tabs and the Title Bar for the sidebar simply add the following in your Firefox Profile. This is not the Local AppData one, but the Roaming one which is normally found at: %UserProfile%\Appdata\Roaming\Mozilla\Firefox\Profiles

You will have a profile folder here, maybe more if you utilize multiple profiles in Firefox. Once you pin-point yours you simply need to add a new folder called "Chrome" in your profile folder and create a new text file "userChrome.css" make sure it is a css file and not a txt. you may have to google how to change file extensions by revealing them in Windows. The contents of that file should contain one or both of the following segments depending on what you want.

/* Contributed by Anonymous user 099626's */
/* Remove horizontal tabs */
#tabbrowser-tabs {
visibility: collapse;
}

/* Remove sidebar header */
#sidebar-header {
visibility: collapse;
}

Once this is done you will have to restart FireFox. Depending on your theme in FireFox you may notice you can't see the windows control buttons in the upper right. To fix this simply go to the "Customize..." menu and check the "Title Bar" option then click done.

ps. I've noticed some FireFox menu's don't take the removal of the Horizontal Tabs into account due to it not being a build in option. With this in mind option screens like "Customize..." may take over your full screen including the TreeStyle Tabs. If this happens simply look for another way to close the screen, which should be provided.

pps. TreeStyle Tabs is a fantastic app that I've used for years, I've slowly started moving to Chrome because of the noticeable speed difference and the large amount of multitasking I have to do daily. I am excited to see if FireFox Quantum can live up to the speed it boasts. That being said...

Happy Tab Hoarding! :D

Thanks to Anonymous user fc7bf5 for fixing the problem to remove the tab bar at the top!

With this fix 5 stars. Strange that the creator of this usefull extension didn't solve this problem.

For anyone having trouble with the horizontal tabs not hiding, Anonymous user 099626's advice worked for me. Create a folder chrome/ in your firefox profile and then in that directory a userChrome.css file containing the following rules

/* Remove horizontal tabs */
#tabbrowser-tabs {
visibility: collapse;
}

If you want to get rid of the sidebar header, add this to the file:

/* Remove sidebar header */
#sidebar-header {
visibility: collapse;
}

You will have to restart Firefox to enact the changes.

Best extension ever that keep me using Firefox

Must have дополнение для ФФ. Пользуюсь уже много лет.

ツリー型タブのアドオンを1年前ほどからずっと入れてましたがFirefoxのアプデにより
ツリーの固定化と最大縮小サイズが狭くなってしまいもっと狭く設定できるようにしてほしいです。
このアドオンを使わないと生きていけない体になってしまい、とても良いアドオンだと思います

Practically essential if you open many tabs. Hierarchical indentation is what makes this superior to all other solutions.

The transition to Web Extensions is excellent considering the situation. There is a current bug on Firefox's end that keeps the horizontal tabs around. You can address this by creating a file in your Firefox profile, \chrome\userChrome.css and add the following rules:

/* Remove horizontal tabs */
#tabbrowser-tabs {
visibility: collapse;
}

If you want to get rid of the sidebar header, add this to the file:

/* Remove sidebar header */
#sidebar-header {
visibility: collapse;
}

You will have to restart Firefox to enact the changes.

I loved having the autohide tabs on the side and no tabs at the top. It was just easier for me when I was search for something, say Thumb drives, and I could easily locate the store page from all the listings I was looking at. The autohide tree tabs on the side gave me more screen space both vertically and horizontally and I miss it sorely. I hope to see this updated soon for ff57!

Auto hide not working in FF57 & display as sidebar! And horizontal tab too displayed.

My favorite extension. Works great with Firefox 57+. It has many options and also allows customization via CSS (I use it to increase font). It doesn't hide top tab bar because of API limitation but for me it is feature not bug :) because I sometimes use also top bar for example when I need more horizontal space.

The reason why I continue using Firefox. Viewing pages in a tree is a great way to keep track of my day-to-day projects.

Such a lovely way to view tabs!