This is (or was) one of my favorite extensions, but then they decide to remove one of the most fundamental and needed features: grouping. It's a basic feature that should be in this main extension, and not in a separated one!!! The developer must have their decision reasons and probably related to maintenance burden... Still I'm kind of disappointed and pretty much lost at least 2 of 5 stars with this removal.

Gute Idee, schlecht umgesetzt (z.Bsp. können Knoten/Root nicht umbenannt werden).

Die Anordnung mit vertikaler Baumstruktur erfolgt völlig willkürlich. Ih empfinde das als sinnlos und macht die Tabs unübersichtlich. Es wäre besser keine vertikale Baumstruktur aufgezwungen zu bekommen.

I get that it's more practical but as long as it is not possible to hide the top bar you end up with double the clutter.

It would be great except it's not impossible under any circumstances to remove the existing tab bar in any way. I tried creating a userCrome.css file since that appeared to be the only way but to no avail. If I have no choice but to have a top tab bar there is no point in having your addon. Shame.

This plugin does a thousand different and strange things like open special tabs to just create a fancy tree, and I just want a simple sidebar.

2-5-20 Review update:
I agree with Korkenwine review, the lack of Tabs Search options is a major missing option. Like many, when doing extensive online researching or shopping, I can easily have over 1K - 2K Tabs open, can get very hard to navigate in TST, do not always have time to go thru & clear out unwanted research tabs daily, that is why TST would be best to stay on top, to help quickly save multi list of ever growing tabs for later.
Again, TST is problaly the best (All in one) extension have found in last few years,but after so much troubleshooting, just cannot get TST to work consistently.
I am also using a fairly new Windows 10 64Bit Acer laptop, (not a 32Bit). I have ( 16GB RAM 1TB STORAGE), so I doubt if my PC hardware is the issue, as even most of the outdated Tabs extensions tested work, but have disabled them, due to lack of addtl options or updates. So my search, (would gladly Pay for even) for the closest TST addon & Full Tabs Mgr continues, until it gets worked out. Cheers!
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Great concept, after trying hundreds of addons, TST has to be one of the top extensions , with most useful features if have many Tabs, & need in user friendly vertical drop down view, for quick navigation & saving, So we do not have to keep installing & removing several outdated junk extensions , that only do a few basic Tab management options in Windows 10 PCs.
**Really wish Firefox & other Top browsers, would create a built-in browser extension like Tree style tabs , with most useful features if have many Tabs need in user friendly vertical drop down view, for quick navigation & desired selection of Multi Tabs saving & bookmarking etc.

Even though Tree style Tabs is a great concept, but like others have said, it just has far too many
Bugs & issues , so cannot even use it hardly at this time.
Like many, I also Used to use the older Tree style Tabs version until it, like most addons became outdated, & full of issues.
Was very excited when this new version was released recently, with many more options, but sadly, have still not been able to get it to work correctly last few most current Firefox versions.
TST loads all of my few hundred Tabs in vertical TST Sidebar, but that’s it, cannot search thru, or scroll
Thru more only 12 tabs out of a few hundred, TST doe nothing, tree style keeps freezing up.
After spending days & hours scouring thru all the Tree style Tabs FAQs, & support forums pages,have always had bug reports enabled, also keep restarting cache, unchecking & rechecking all options, many times, to no avail.
Like many, just do not have nay more time or energy to diagnose why TST addon not working still.
***Would be great (if TST Developers put in a Built-in Errors & Bugs troubleshooter & Fix option) so we do not have To keep trying to figure all TST's issues & bugs with each Browser version update.

Again great concept, could be the one of the Best extensions ever, if developers could
Work out all the ongoing Sidebar Tabs issues & bugs, most other Tab Managers do not have all these issues, So can finally use TST, without all the ongoing headaches.
My online Reviews of Tree style Tabs Rated ( 2.6 out of 5 Stars).

Great extension while it is running, but each time the firefox is restarted it's a pain because all tab hierarchy is broken.

Need a feature to auto-backup and manually save/restore tree.

I thought that the giant grey bar it makes is intrusive, also I dont like it zooming out the page at at. A transparency setting would be great. Ways to make it smaller and less intrusive to the website would be nice as well.

This extension bugs out a lot, forgetting the positions or tabs between plugin crashes and even between F1 sidebar toggle presses. I LOVE it when it works, but I HATE it when it doesn't, as it takes at least 5 minutes to fix the mess it creates when it breaks. (All the tabs are randomly ordered, parents forgotten, some tabs are even missing from the tree altogether and exist as "ghost" tabs between ones actually in the tree!)

Brilliant idea, poor solution. Unstable a buggy in all versions.