NOTE THIS EDIT: I just noticed configuring TST and following it's advice of changing configuratin 'browser.tabs.multiselect' to true, but it didn't exist! This is 77.0.1 64-bit Linux version and that option didn't exists - I added it, but as it was not there to begin with, I doubt it will be of any help that I added it... Advice?
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Awesome! I used to love an old legacy add-on called Tab Mix Plus, which really is an awesome add-on for the tab bar, but now I love the tab tree much more - it's also specifically nice with small netbooks, like my Acer Aspire One D270 (old, I know, but still works marvels if not put under too heavy strain), that have a widescreen display and very low vertical resolution - you can hide the sidebar if you need to, although most of the time it's not a problem, and you save the height of the tab bar in vertical resolution available to show the actual page. With such small displays it really does matter a lot.

Edit: Many people are complaining about the lack of search function. I'm not sure what exactly they mean, I'm completely satisfied with being able to search tabs using the location bar - you can enable this from FireFox settings. However maybe a search function that only shows the matching tabs (and the tab-tree they are part of) in the sidebar - when it's empty it would show them all. I can't think of another way they mean, but I'm really fully content with searching for the tab using location bar anyway :)

It's a must-to-have!
Would it be possible to add an optional vertical scroll bar? Or a way to speed up scrolling using the mouse wheel (w/ a key modifier), at least? It may take ages to scroll from bottom to top tabs when there's a lot of tabs.

Initial testing is good. On first install, it doesn't look like to captures the current tree-state of the open tabs (may be my setup?).

Still to see if closing a tab in the intermediate tab stack loses the tab connections (may need 'Tab flip for Tree Style Tab'?).

Have tried the closing of an intermediate tab and it shrinks the tree, rather than remembering the call stack.

Extremely helpfull Add-on. Helps in any kind of research or just by sorting the 20 tabs you have open. The only thing that is missing, is the option to save tabs with the hirachie. That would be super helpfull, if you want to continue your research later.

Nice extension overall. There are a few minor tweaks I wish it had but nothing too big.

GANZ WICHTIG: Ich möchte die Tab-Leiste schmaler ziehen, aber das geht leider nicht. Ich würde es gerne so schmal ziehen, dass man nur die Symbole sieht und Lautsprecher.

A must have extension. 4-stars because of some features I would like to have:
* navigate to tab group instead of individual tabs with Ctrl + (number)
* renaming tab group

to.pure.makeup.to.let.something.in.pure.idea.clear.convident

really cool addon but i really hate how it opens a new window all the time and i do no know how to turn that option off. it also takes up a lot of space on the screen.

This plugin is fantastic and I really really like it!

There's one change I'd like to see changed, I completely agree with the name of your plugin and it works super well in a lot of contexts, but it's a bit problematic in the Tree Style tab itself.

You see, the name is so long, that It pretty much always gets clipped as you can see here in this screenshot.
https://i.imgur.com/UI9kX37.png

I would argue that the name "Tabs" is more than enough and a tad cleaner.