I first wrote the review below in 2019. The add-on hasn't been updated and it's functionality hasnt' changed since then. I still use it to manage tens of thousands of tabs between multiple profiles. It's infuriating when it occasionally loses tree structure in individual windows and sometimes the restore doesn't work so you have to manually re-group (no tabs are ever lost), but it still saves me hours of messing around, every day.

2019 review:
I don't know why 'Tree Style Tabs" is recommended by FF and this isn't. This addon leaves TST for dead and is by far the best tab manager I have come across in a thorough search and test.

It is so superb that a manual of all the things it can do would be helpful! The basic sidebar setup with drag-and-drop can be instantly used by new users, but it can take a lot of time to find and figure out how to use all the other brilliant parts of this addon.

It has multiple backup options- customisable session autosave, EXTERNAL save a group or whole session, import between profiles, merge sessions. Of all the features in this addon missing in other tab organisers, this is the most important. MISSING in tree style tabs. TT's bookmark feature creates tab indexes for saved groups and sessions, structured by group, folder and trees. (Or Onetab - save, restore in new window, Onetab.)

Can use TT search in each window to select and drag tabs by title or url between groups, folders and windows. (Use Conex for cross-window searches by container, or Fast Tab Switcher by visited time.)

I use TT combined with profiles as a task management system, managing thousands of tabs. Profiles for areas of work (to keep memory manageable), Custom named groups (thin vertical tabs at the left, can be hibernated when not in use) for categories, custom named folders in those groups to divide tasks (and comment on them!), and finally trees for subpages so I know where I am.

Lots of useful options for groups, folders and trees-- collapse, suspend, reload, bookmark, hibernate, search, duplicate tabs. Customise where different types of new tabs open.

Highly customisable UI: tab height and indent (Yay! fit heaps in sidebar, minimises scrolling), colours for hover, active, selected, search and combinations of them, 1-click save customisations.

AND it imports tabs unloaded - so memory and custom tab titles are preserved until the tabs are loaded. (Bookmark imported groups or sessions before loading to retrieve custom tab titles with Tab ReTitle addon.)

The only major thing missing is container support! Only 1 tabs manager has this (Sidebery, but it's structure doesn't work for me), it is SO needed. (Though merge does keep the containers of the previous tabs, other imported tabs have to be reopened in new container which loses their place in the tree structure - you need to import in a new window, bookmark the import, save the session, reopen the imported tabs in containers, manually rename the custom titles, then merge the saved session and hope it works.)

A few bugs in a some of the advanced features, a headache but those features don't even exist in other managers.

29/9/20: I am marking this down to 4 because I am SO SICK of spending days manually fixing lost/moved new tabs/trees/groups/sometimes entire session structures. Occasionally, randomly. neither restore nor merge of backups works and the dev has done NOTHING in over a year to fix this bug, or to integrate containers, and STOPPED someone else who tried to. I'm going to mark down 1 star each time I get mad enough to visit.

PS it DOESN'T unload tabs unless you select tabs and click "unload" in the context menu. The previous reviewer is probably talking about a feature recently introduced in FF.

Was really enjoying Tree Tabs for 2 years until it began loading/unloading all the tabs at a 1 hertz rate. Tried to fix the problem by deleting files, reinstalling, etc to no avail. Seems it got triggered when using export/import feature. Kinda a shame having to abandon the extension for Tree Style Tabs. The developer seems to no longer support it.

Near-perfect in its simplicity. My only quibble is that I don't think it has the ability to hide hidden tabs, which would be nice.

Если выделяя вкладку чуть шевельнуть мышь, то открывается новое окно браузера и туда переносится эта вкладка и все дочерние. И если их много, то все зависнет.

If you move the mouse slightly while selecting a tab, a new browser window opens and this tab and all its children are transferred there. And if there are a lot of them, then everything will hang.

Has to most features compared to other extensions and is very responsive. Sadly it seems like the extension is no longer maintained. The license prohibits derivatives so it's impossible to continue developing this extension.

Looks nice, with several features. It might even have what I'm looking for, which is to save and update multiple windows tab sessions, but after more than one hour with it, I still don't know even if it has that (others were really intuitive without any learning curve whatsoever). And there is no instructions. Looking for another one, 4 stars because it is difficult to find an add on with the tree structure though, and I'd like the developer to continue working on it...

Sometimes the tree structure of sorted tabs gets lost, which is really annoyning. The backup feature does often recover this, though. I've tried a couple of similar add-ons, but I'm always coming back to Tree Tabs because of its many useful features. Hoping for a new, more stable version.

Of the minuses:
-No general tab search across all groups.
-Auto sort by template does not work
-Skinny setting hotkeys

Great and essential Add-on ... better than Tree Style Tabs. However, Automatic Tab Assignments has stopped working (even tried on a fresh Firefox install). This was a big help keeping tab-sprawl at bay, as now I have to manually keep moving my tabs around. I'll keep using it as long as it's mostly working, but I'm sad that development seems to have stalled.

Was great, now constantly flashes "Session did not match and will not save. Click here to reload" and automatically reloads the sidebar every second or so. Completely unusable right now. Seems to be a common theme.

EDIT: I do start with previous session. After ticking that option and restarting FF, the sidebar loaded ok. un-checked it, opened a few tabs, restarted again, and all is still good. Back to 4 *.
Will rate 5 if you give an option to not flash the 'tabs saved' text at the bottom. it is always catching my eye and distracting me.

Just installed this. looks like it will be super-useful. I did spend time clicking on all the menu buttons, but still unclear on:
1) how to set up groups and folders and how they differ from each other.
2) how to color individual tab rows
Is there any type of User Guide anywhere??
Thank you.

Tree Tabs sometimes repeats loading.

Once Turn off "Discard tree structure after browser's restart" option, and turn on to it will be fix.

5 stars because it does its job well and there is a lot of features available.
Minus 1 star because in terms of default (I say default because you can customize the theme) ergonomics, it could be better.