after using this, and accidentally found another add-ons called Sidebery. I think this needs to be developed further, because what is here is in the sidebery and even more features. Don't know why Firefox recommends these add-ons more than Sidebery

UPDATE 3-STARS: Frustrating that a core function to group selected tabs has been removed and now requires a separate extension to be installed.

ORIGINAL 5-STARS: Great extension, love that it can be extended by other extensions too.

Jul 1, 2021 - MANY BUGS:
- frequently crashes and "restarts" add-on and sidebar... I tend to have 500+ tabs open (currently 1600+)

- for some reason sometimes tab tree opens into a new window when I am simply clicking tabs in sidebar.... and I DO NOT even have the "Tree Style Tab in Separate Window" option added

Enhancements needed:
- need to improve the highlighting of which tab is the current active tab.... something like a black border... including when using with Colored Tabs

- need a command to be able to separate 1st tab from tree... instead you have to move all the other sub-tabs

Nov 28, 2019 - please add search function/filter to tabs - I see this was just added as of Jun 2021 - YAY! (looks like still beta version though but nice move!)

Aug 9, 2019 - Please add keyboard shortcut for Mac, preferably one-handed, e.g. OPT-1

Version 4.2.2 not working. I downgraded to Version 4.1.11 and no update ...

Seems when i restart firefox the connection to the parent tab is dropped, so structure end up flat again. A bit annoying, and looses a big part of its function. Otherwise a nice addon with potential.

It's wonderful to work with tabs in a tree in the sidebar. However, there's a frequent bug appearing: sometimes the last tab or the one before the last one bring you to the incorrect tab (and reloading the extension/sidebar doesn't work). Other times it won't let you change tabs at all (clicking, ctrl+tab works fine), or hang unexpectedly until you reload it. It's not reliable, but when it works is quite useful.

I have three recurring bugs, and they're ones reported by other users. Firstly, the tab sidebar often doesn't load and just shows the loading indicator forever. Secondly, it can get into a mood where clicking one tab switches to a completely different tab (often the tab directly before it in the tab order) (clicking the tab in Firefox's default top tab bar instead works as expected, so the issue is definitely with this add-on). Thirdly, it often forgets and rearranges child tabs with no apparent logic, changing the order and hierarchy completely.

I rely heavily on this add-on so I'm hoping they can fix these issues. It would be an easy five stars if I could just trust it without worrying whether or not it'll even load! I want to remove the default tab bar and just use this add-on, but at present I can't trust the add-on to work properly.

Not works very well on mac firefox, no any tabs show up but just a loading indicator keeps loading forever. This doesn't happens everytime, but still very high frequency. Althrough I can get rid of this by disable and re-enable it, it's still anoying

WARNING: This addons is currently very buggy. Usually, it's a simple case of clicking a tab and a completely different tab is selected, every now and then. This is solved by going into Tree Style Tab's settings and unchecking and checking the "optimise tree restoration with cache" option. But today, I leave Tree Style Tab at the wayside, as my entire 70+ tab tree structure was completely demolished when I opened up Firefox for the day, only to see all tabs being considered direct children of 1 other tab, disregarding any previous tree structures. Disregarding the fact that I should probably get my tabs sorted out, it is clear that Tree Style Tab, currently at version 2.8.5, is too flawed for my uses. Tread with caution.

Can you
1) create an option to FULLY disable tree structure?
2) Add folders?
I just want to have vertical tabs, no any trees.

You need to urgently remove/move/add possibility to remove the "Close tab options" menu in the context menu. Now it can be accidentally triggered to close all tabs when actually trying to reopen closed tab! Just lost over 50 tabs doing so!

Otherwise the add-on is great and recommended for anyone with high number of tabs open.

It'd be a true gem, if someone could change the tabnames so that you don't see the

Nuts...doesn't work with Colorful Tabs like it did in the old Firefox.

В Tab Tree было авто скрытие панели владок, переключение по клику между двумя вкладками. Этого всего очень не хватает.

This is a love-hate relationship. The concept is great. The implementation is horrible.
Sometimes this add-on just mixes up the hierarchy of my tabs and I painfully have to reorder them by hand. This can be a lot of a work since this add-on espeacially makes sense when you use many tabs.

When it works it's cool, but sometimes it just keeps loading and nothing happens! Now I have 3 tabs open and its been 25 minutes, still it is showing the loading animation, 25 minutes to load 3 tabs is not right. Very nice add-on but very buggy. The only solution is to close the tree style tab sidebar and then again click "show sidebars". Then it works perfectly. Hope its updated soon.