Best Tree Tabs extension ! And I've tried several !
This one groups the most features I need :
- Tree view
- Tabbed Groups (it would be nice to be able to select background colour of tab like in Opera)
- Pined tabs at top
- Themes (you can create your own one quite easily)

And more !
I also use this one with Opera ;)

Thanks for this great "must have" 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.

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 I am still not sure if I have found and figured 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, reload separately or merge. Of all the features in this addon missing in other tab organisers, this is the most important. (You can use Onetab to create tab indexes for saved groups and sessions - save, restore in new window, Onetab.)

I use it 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).

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.)

A few bugs in a some of the advanced features, a headache but those features don't even exist in other managers. A very good issues site and responsive dev who keeps working through them.

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

Good addon with many useful features. Best vertical tabs addon.

Also, completely unreliable. Yesterday, for the 20th time probably now, my browser started with all tree structure completely gone and all the tabs in the "Ungrouped" group. Reloading addon does nothing in this case. I had to set up full FF profile backups specifically because of this addon, since it fucks up all the time.

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.

After some months of treetabs missing in the sidebar, it has suddenly reappeared, with all 300+ tabs still in order!
I'm so happy about this uber helpful addon getting back on track!
My donation is meant as a big "Thank You!" as well as an incentive to keep on caring about this georgeous baby.

Definitely the best vertical tab extension. Has so many functions that I could get rid of 4 other extensions and use only this one. There've been no bugs or loss of tree structure. Amazing theme support too...

Great bu buggy...
the tabs all appear in the same group (loss of structure).
Plus various bugs monthn annoying.
And sometimes all the tabs disappear. This morning, I lost everything, it's not acceptable: I give up to find something more reliable.