I was looking for the ability to sort my open tabs via a firefox add-on/extension. I found this. Sorting isn't listed as a feature, but Tree Tabs effectively allows this.
Two Steps: I search and put the matched tabs in a group.
This tool seems better than the ones that just offer sorting. Just started using it today.

There was a bug.
Version 1.7.6
1. When adding a new tab, the tab is added, but it is not displayed.
When restarted, it is added to the bottom of the group.
The occurrence condition is unknown.
There is no problem immediately after rebooting, but it will occur again after a while.
I am setting to add all tabs as child tabs.

2. When tab group was imported, the tab structure was broken.
Also, "Rearranging tabs and folders" does not end.
It was not possible to open it by clicking the tab, and when restarted the tab had disappeared.
After importing it back to v1.4, it worked.

!
Oh, there was such a place.
I will report it when I find a bug in the future.
Thank you for maintenance.

Tree Tabs is easy to use, simple, but really useful when you need to manage a lot of tabs.

You can organize tabs in a tree structure in the sidebar. Fold it or unfold it. Navigation of tabs has made simple.

Wow, this is VERY promising and I'm already using it full time. If the bugs get ironed out this could be one of the most popular extensions for firefox.

I've been using this for quite a few months, and the developer has added some very nice features during that time. Organisation of tabs is a breeze with this thing.

I can select tabs without loading them, put tabs into general organisational groups and trees under each other, close and move lots of tabs at once, and so on. The tabs are also displayed pretty compactly by default, and additional information (such as whether or not a tab is loaded) is well conveyed. A number of these features cannot be found in some of the more well known tree-like tab extensions, which is why I use this one.

Would it be possible by an option to change this shortcut key ? *Ctrl+F2 to toggle Tree Tabs sidebar*
I would love to use Ctrl + Q, if possible, in a future upgrade consider for this option :)
Thank you very much, this extension is wonderful!

I FOUND IT!!
Now IMPORT can open!!
THANKS A LOT!!!

Awesome add on ! Seems to be a great successor for tabkit 2 !

Some ideas and remarks :

Color tabs when a child tab is opened , I mean that each tree could be colored in a different color : it's very useful ! (a click on a link opens a new tab in the same color of the current parent tab, the main parent tab is colored only when a child tab is opened) .

Highlight tabs in a special color for links opened in a new tab but the tab haven't been opened/clicked/viewed.

You could also add a checkbox for "mousewheel scroll on the last tab allow to return to the first one".

Shift + mouse scrool to switch between groups

A keyboard shortcut to close a tree could be nice too ;)

Add a tutorial on the add-on web page to explain how to remove the original horizontal tab bar from firefox.

Thanks for the work on this add-on !

The only extension seamless combining tree style, folders and groups. Also theme customization is amazing.

Great add-on. I'm still not a big fan of horizontal tabs but I'm sticking with it until a real a «Tab Groups» alternative comes about. The ones that exists have many problems that need fixing.

Of the "tree tab" add-ons I've tried this one has the most feature sets I'm interested in. Most important >Tab Grouping... Tree hierarchy, Tab Unloading, Searching, Sorting are just really nice features. The latest version can now 'hide' tabs when you switch groups without closing them so now it even more useful. You can switch tab groups and then hide the sidebar if your strapped for screen real-estate.

After «Tab Groups» etc. died because of WebExtensions I had to find some good alternative and settled with this one. It is so feature rich that I consider contributing to this great Tab Manager

Much less buggy than Tree Style Tabs. Also I love the search tabs feature and it seems to be more lightweight and more responsive than TST

Kroppy, you've done all us FF users a great service - THANK YOU! As a long-time user of Tab Folders (and all the various add-ons that worked up until WebExtensions killed all the great add-ons I'd used for years) I was in limbo until I stumbled on TT. You've given us all a way to organize the dozens of tabs and access them easily. And you listened to all of us begging for folders and groups and you built that in, as well.

Now I just need an idiot-level tutorial to figure out how to USE all these marvelous tools...

Great add-on, cannot live w/o it - nicely replaced the old tab groups manager & helper. Feature request - is there a way to allow right click the tab and let me save bookmark?

EDIT: DON'T INSTALL TAB SESSION MANAGER.

Kroppy, thank you very much for the tip. After removing TAB SESSION MANAGER, your extension now works perfectly. Maybe adding that information to the description and/or work with the owner of that extension to make both compatible.

This is the most wonderful extension for Firefox, period.

First impressions: I'm just now testing Tree Tabs, as a long-time Tree Style Tab user who's followed Tree Tabs from the first Vivaldi forum posts. It has some very nice features out of the box. I love the groups, unloading, and session backups, as well as the auto-correcting tab order for keyboard shortcuts.
Additional thoughts: So far, pretty awesome. Literally replaces three extensions, and very nearly three more, at least. Groups, tree-hierarchical tabs, and tab search are fully replaced, and it almost replaces a session manager, tab-unload manager, and an undo-close menu.
If wishes were... : It'd be helpful to have the session feature save automatically every x minutes and allow selection of a session to load. Tab-unloading would be more useful if it could be automated on a timed basis with a whitelist. Undo-close would be nifty if it had a list of the last few closed tabs, but it works fine as-is.

Bugs: None found yet?
Noteworthy: The audio icon only appears on that specific tab, even if it is within a collapsed tree. This can be a bother if more than one tree or branch of possibly-guilty tabs exists. It might be better to display the icon on the nearest visible parent tab, if the playing tab is hidden, as well as on the group title, to aid in locating an offending tab, especially in cases of sneaky, ill-behaved ads, but also for those who (over)(ab)use YouTube and the like.
Edit: Found the sidebar unresponsive at times. The problem was predictably resolved when I disabled my session manager and a tab-unloading addon. Seems that many (most?) things that interact with tabs directly may interfere with Tree Tabs.