It's not simple at all

4.8.1 version. Activation used 15MB RAM (only RAM, not total memory.) Full page tab group manager is only presented in bright white. -- even though I followed the instruction for setting svg.context-properties.content.enabled . User browser configuration has no effect. Group management tab shows as constantly loading.

Eigentlich eine gute Erweiterung um auf Themen bezogen die Tabs in Gruppen zusammenzuführen - jedoch: Mich jedes mal beim Gruppenwechsel erneut (z.B. in Youtube) anmelden zu müssen - das geht gar nicht. Ich werde jetzt die Themen auf verschiedene Browser verteilen müssen - zum Teil gibt es dort eigene Lösungen um Gruppen zu bilden. Das Add-On habe ich jetzt entfernt. Schade ...

Um add-on que se comporta de forma muito estranha. Parece bem bugado. Usabilidade deixou a desejar muito.

As some others have reported:
When I group some tabs, the tabs I have not grouped gets hidden. Why?
Why hide tabs on my screen.
I have to click some unload button to somehow maybe bring them back.

Overall feels buggy, or weird. Discard button does nothing. Bug?

I used it for two years, and I'm done with it. When it works, it's good. But as others have reported, without explanation, saved tabs will disappear without warning, showing a 0/0 for nearly all saved tabs.

At the moment I'm really disappointed that a plugin that is so hyped is not able to manage pinned tabs as well?
Why am I so disappointed?

I need access to a huge number of tabs, from different themes per window, sometimes 30 + x tabs per window, with 5 windows (themes).
Now I had hoped, through this add-on, to at least reduce the number of open Firefox windows, by switching tab groups, back to one window, since tabs in multiple rows no longer exist, thanks to Mozilla and the (crappy) web extensions, which are only useful from a security point of view. Only unfortunately, the web extensions have been forced on users in an overhasty and immature way (but that is NOT the fault of this add-on).
If this add-on also had access to pinned tabs, I could now conveniently switch between groups of tabs and would be willing to give 10 stars, so I give only two, because the idea is good, only its execution makes me shake my head.

If someone really needs many tabs of a topic area, between which one can switch then fast by click, then one is forced to pin these around without scroll orgies in the table bar to navigate.
And there you are offered, with the STG add-on, an actually ingenious solution to this problem and then this add-on does not have access to ALL tabs? An add-on whose only purpose is to handle tabs! Yes, it can not recognize the pinned tabs apparently, that is probably the worst joke you could think up.

Very buggy.
Tabs were duplicated a LOT, clicking on a tab duplicated it. Opening a new tab group created multiples of every tab.
Not fit for purpose.

Convenient, until it isn't. Duplicating tabs even after full reinstall, suddenly I had 190 tabs out of 19 in one group, and this happened in several groups. No idea why or how, but it makes it almost unusable.

EDITED REVIEW: Breaks Multi-Account Containers (github issue 990), potentially massive security issue, especialliy since broken tabs report insecure connectivity to source. PREVIOUS REVIEW: I think it is great, and it is so nice to have my tab groups back. I would like a couple of options regarding UX but I can raise those separately in the github, I am sure, but the main one of those is an option that when you tap a group it opens in a new Window. Otherwise, once you have it setup to work how you like (I advise no 'auto' creation) it is a silent system winner, and great for productivity as you can silence different workflows and come back to them as if you never left. Unlike chromium tab groups which are always there, staring at you ;-).

It is a little bit buggy. Sometimes tabs will open multiple times and make huge mess.

too intrusive. OneTab does not requires so many permissions.
https://addons.mozilla.org/en-US/firefox/addon/onetab/

My comments in Portuguese and English:

Justamente por ser "Simple" Tab Groups, é prático para usuários comuns que precisam de praticidade para organizar numerosas abas abertas. Você cria grupos e os identifica como achar melhor, e em seguida arrasta para dentro de cada grupo as abas abertas, de acordo com os assuntos.

Por outro lado, uma grande desvantagem desse complemento é que ele força você a ocultar as guias agrupadas.
No agrupamento de guias do Chrome, seu grupo aparece como uma única guia que pode ser facilmente expandida e recolhida quando você deseja mostrar/ocultar todas as guias pertencentes a este grupo.

Precisely because it is "Simple", it's practical for common users who needs practicality to organize numerous open tabs. You create groups and identify them how to find better, and then drag into each group the open tabs according to the subjects.

However, a major drawback of this addon is that it forces you to hide the tabs that are grouped. In Chrome's guide grouping, your group appears as a single guide that can be easily expanded and collected when you want to show/hide all guides belonging to this group.

It would be great except that it keeps all your tabs open between sessions even if you set firefox to open a fresh session. If not for this I would give five stars. As is it is unusable.

Sadly it quite often drops all of my tabs and I need to manually add them back in. As far as the design goes, it's quite nice. When it works, it's useful. It's not as intuitive as the group tabs in Chrome, but that's a problem I have with Mozilla, not this extension. However, not being able to change the location of backups is really grating on me.

Questionable decisions:
1. removing groups will close tabs (!?!)
2. once I opened a group, I could not find a way to return to the non-grouped tabs.
Also, you cannot have multiple groups opened in the same browser window.

It worked the first day, and it hid all the tabs I chose that day for a while, but then yesterday the extension broke and I couldn't open the extension's menu, the extension UI didn't show up when I right-clicked on a tab, and then all my hidden tabs just popped up again at one point. I kept getting some error message and I didn't know how to fix it, so I uninstalled the extension and reinstalled it to see if that would fix it, it didn't.