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.

Came to it as a replacement for Tab Groups when Firefox Quantum stopped supporting that one. Was great while it worked, but now it just shows the loading icon forever; both on Linux and Windows. EDIT: After update works perfectly again

Works perfectly. Thank you.

I was worried that after quantum that treestyletab will be dead. However, the dev did a great job finding a way around it!

Seems promising, but in reality it’s not so great. I tried using it in conjunction with Simple Tab Groups and found that after changing to another group and coming back it had spontaneously created its own sub-tree group of (presumably) all unloaded tabs. It’s not clear how you can even undo this short of closing all the tabs it contains. Extensions shouldn’t do unexpected things like this. It also seems fairly CPU and memory intensive at times.

Another problem is that it doesn’t seem possible to organise open tabs (through drag and drop) without loading each individual tab. This makes it pretty useless as a utility for organising already open tabs.

F1 is a terrible choice for a shortcut.

If you use it from an empty Firefox, it will probably work as advertised, dutifully creating trees, etc. But if you already have lots of tabs open that you want to organise, this will do little for you.

Sadly, currently broken.
It guzzles memory and CPU time like nothing else I've ever used and really slows down the browsing experience. This addon should *not* be going to 80% CPU usage and adding 2-4GB of RAM usage just because I opened a single tab.

I hope it gets fixed soon.

edit: My mistake. The real cause of the problem was one of the settings in the Tab Session Manager.
5/5 for Tree Style Tab itself.

A must-have add-on.

So glad to see this back in Firefox Quantum

Inserting new tabs do not respect preferences set in this addon for Firefox Quantum. It appears the plugin does not actually respect any of its own settings. If I press CMD + T on Mac, it always goes to the bottom and makes a new tab tree. Never does it make a child tab.

Earlier, before FireFox 57, was such a cool addon, now everything is bad: - loads the processor to almost 90%, does not open tabs when i start FireFox, i must to disable and re-enable the add-on. Loads memory-from 2.5 to 6 GB (with twenty tabs). Locks pinned tabs periodically. I also agree with other users regarding the lack of functionality that was there before, and unnecessary semi-loaded tabs, tabs opening at the top of the list rather than at the end, problems with restoring tabs.. nothing works.

It totally changed my internet browsing experience! I don't need to search where was that tab. I know where I got there from (on which page I clicked a link when new tab was opened). I know which crappy site opened a new tab without my permission. I can close whole "topic" of tabs. It is like the already existing tab-groups but evolved onto a higher level and on steroids. Problems? There are some: firefox memory limits and the fact that my browser often has 1k+ tabs opened at a time. Over a thousand - and it still works :D Don't try this on chrome or safari. Not even mentioning IE. TreeStyleTab is just great. And user experience is nice as well (Piro provided links on how to deal with UI restrictions - could be more permanent/readable but it is there.... to solve issues that he couldn't do on his own).

A great add-on. May I propose an idea? ) It would be great to have, as an option, side-tabs colored depending on tab domain.

Removed dark theme (WHY?!??!), still limited vs what it used to be before quantum.

My favorite addon! Though currently when I reopen my second window, it usually forgets the tab tree structure (un-indents all tabs). Otherwise it's perfect.

Vastly improved my tabbing experience. A must for everybody!