I love this Add-On... use it and abuse it...
It does take a bit of practice and learning, but it sure works for me...
Only thing I hate is... I can not get rid of the Tab Bar at the top of the browser...I see no point in having it there....
Is there a way to turn it off?

This is great if you have opened like 10 more tabs.
But I love to auto show/hide if it more than xxx tabs open.
Is this possible?

useful replacement for the old tab groups extension. However, it's slow, and on every second addon update it mangles my tab groups.

EDIT: I take it back, it just fixed itself :)

Great Web Extension and only missing one star from perfect as occassionally it just seems to hang when FF is first opened with10 or more tabs opened. I then have to close the sidebar, restart FF then enable sidebar again.

Very good idea but there are some issues with recognizing "pending" tabs. They should be red according to my settings (and it already worked for a short time) but they just keep the style of regular tabs. With over 300 open tabs, this is unfortunately not funny if you don't know which tabs are to be visited yet. With regular CSS and (userChrome) and FF tabs it works like a charm though.

This is an invaluable extension, seriously! It's one of my biggest practical reasons for using Firefox. However I have noticed that the tab context menu doesn't always show options that should be added by other extensions, which is quite annoying. Oh well. This is a fantastic extension still and I'm grateful it's being updated :D

Great, must-have addon, and first reason to using FF for me.
- Tst toggle hotkey change option is needed. f1 by default, srsly?
- Tab context menu needs custiomization too:
-- missed some important options from tabs (Send to other device, etc);
-- ... but its overloaded with items that I would like to disable

Also some occasional errors: seens descend background tab sometimes opens in wrong tree; multiple tabs closing sometimes breaks on halfway

BUG report: 3.9.21 broken, reverted to 3.9.19 and that fixed it.
When it works, it works. absolutely necessary.

Tab Tree was better. Too bad about ff>55

I really love this extension because it makes organising my tabs so much easier and logical. One issue though is that when I restore tab after a crash, I lose all the trees. I have to manually make the trees again which can be pretty annoying. It would be fantastic if you could fix that

UPDATE 7/12/21:

Since my last update a year ago, pretty much all problems of which I was aware have been fixed.

But since the last update (or maybe the one before that--but recently, in any case), a new one has cropped up:

When coming back to a Firefox session from Windows Sleep mode, TST has unloaded, and the main toolbar icon is gone. I've also seen this happen after a Firefox restart or crash. Going into the View menu to re-enable TST doesn't work, as it's also gone from there.

I've noticed at least one recent review that reports this problem when "starting Firefox."

The only work-around I've found is to open the Add-ons and Themes page, disable TST, re-enable TST, then go to the View menu to re-load TST in the sidebar.

It's a recoverable problem, but it's a pain to have to do this every day (and some times two or three times a day).

UPDATE 7-21-20:

Since the last Firefox update (to 78.0.2 64-bit), almost every time I left-click on a tab in the sidebar, instead of just selecting the tab, TST executes the "Move tab to new window" action. If the tab has children, the entire tree is moved to a new window. (I say "almost every time" as there may be one time in about ten that TST does not do this).

Needless to say, this is extremely annoying, as I then have to move my tabs (one at a time) from the new window back into the original window.

If I remember to do so, I can select tabs normally from the top tab bar, but muscle memory is ingrained for TST's sidebar, at this point, so I frequently forget to do that.

I don't know if this problem is due to a change in Firefox or in TST, as I'm clear on how their latest updates might be interacting. I can say that TST v3.5.13 did NOT fix the problem.

UPDATE 12-31-19:

The parent/child tab separation happens rarely now (and it's been a few months since I've seen it happen, so that bug may have been squashed.

ORIGINAL REVIEW:

Works pretty well, but sometimes child tabs get separated from the parent tab and other child tabs, with non-associated tabs in between. I've not seen a pattern to when this happens, unfortunately. At least the tabs are lost, but it can get confusing.

There is only one thing I find annoying about this extension: it automatically creates child-parent relationship between tabs which are opened from previous tabs. I'd rather have full control over tab-grouping (group them myself) than having the extension group tabs in a way I can´t even control from the options section.
Other than that, this add-on is the main reason I stick to FF, keep up the great updates!

Estoy empezando a utilizar este navegador y me ha gustado. .
De momento 4 ⭐

This new web extension is really disappointing and lacks the features of the original add-on.
I can't have both bookmarks tab open AND tree style tab open at the same time, which is a big letdown for me.
I can't close "all child tabs" at once anymore by clicking on the right click menu.
Can't close multiple tabs at once with a simple middle click on it as it always asks if I want to close multiple tabs before, which previously didn't for middle button.
When I close a tab, it tries to get the focus to the one under it (hence loading it), instead of the parent tab, and only half loads them (so that they remain buggy forever, until reload)
Also it doesn't work well with SNAP Links Plus, which, for some reason, creates useless temporary tabs with some weird indentation.
A lot of options disappeared from the add-on as well which makes it look like a watered-down rip-off of what it used to be.

EDIT :
The behavior of this add-on changed for the worst in the latest patch.
It now auto expands ALL the children and ALL their descendants upon tab selection (and not just those that were expanded before, like in previous versions)

There's no way to revert to the previous behavior and it's really annoying to have those huge FULLY expanded threes I didn't ask for.