My productivity has improved so much with being able to have different tab groups for work, personal, research, volunteer work, etc! Great way to get in the zone and not be distracted by other parts of your life.
I have had it crash a few times, but when I close firefox and reopen it, all my tabs are still there so it's not a big deal. Be aware that it makes backups in your Downloads directory (starting with STG); you can delete the old ones at any time or disable this in settings.

Takes a bit of learning to figure out, but once you're comfortable using it, it's great! Love that it hides the tab group you're not using: less temptation to switch tasks.

It's been great up until recently - I'm having the same problem other users are reporting, in that tab groups disappear when restarting Firefox. I can click on the Tab Groups button and select a group and they will reappear, but my pinned tabs are missing. Needs an update, I think. Last update was 9 months ago at the time of this writing.

The idea is nice, but I feel misled. It said it "works like chrome's" but the one in chrome collapses and opens with a simple click. I feel like once I have a tab in a group I better not hope I can access it ever again. Clicking on the link just make the page refresh. Again, not cool to claim it's "like chromes" when it really isn't

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

Put all my tabs into a group, restarted firefox, the group no longer exists.

STAY AWAY IF YOU WANT TO KEEP YOUR TABS!!!

works well, feels like using safari tab groups sidebar

Simple Tab Groups? I suppose it's simple to use but it's anything but simple in functionality! Wow. What can I say? Firefox actually works, unlike Safari and this extension actually works, unlike Safari's tab groups. This will change how I work and browse. Thanks!

I did not install this extension because once I saw how much data it collected and what it wanted access to, I was quick not to allow it. Why does it need access to recently closed tabs, access to download files, read all website data? C'mon... this was one of the only tab grouping extensions I would have use too...

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

It would be great if the developer could add "subgroup" functionality to the extension. I right now have 65 groups open lol. I would love to be able to put each groups into categories. For example., if I am doing research on topic X, Y, and Z, and have groups named X,Y, and Z (respectively), I would love to be able to put all three groups under one group called "research". Hope that makes sense. I'd hazard a guess that this shouldn't be too difficult to implement. Many thanks to the developer for this extension, it has made research so much easier.

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.