This is GREAT!
This DO work just fine in private browsing, and its NOT slowing down anything.

Thank you so much!!!

I appreciate this addon. It´s wonderful. But I have got FF60.0.8ESR, and I cannot use it, because addon requires FF65.0 no ESR. I assume it works for a lot of older versions, but it seems to be hardcoded. I have not got an email address of the developer, so I try it this way. br Hans

Really, REALLY great addon. One of the 3 most important. The only issue it has is that it doesn't play well with Panorama Tab Groups (https://addons.mozilla.org/en-US/firefox/addon/panorama-tab-groups/) and will often throw tab focus into another tab group when closing a tab.

I used it for 19 days.
Once I lost all the tabs.
Today it was not showing any tabs, although they were not lost.
I reinstalled it two times to no avail.
My ideal addon would show multiple rows of tabs in the tab bar, with a different color for each group of tabs.
I managed to have that by using the chrome directory, except for the colors.

Nov 28, 2019 - please add search function/filter to tabs

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

Adorei a extensão e a forma com que foi organizado. Perfeito. Apenas um desejo: tradução para português Brasil

A usefull addon that not working very good. Now, I can't move the bar to right. At left place is for people who use their left hand. Tabs are not scroll with mouse.
Firefox 69

If you're looking for perhaps the most transformative workflow addon for a web browser, Tree Style Tab is undeniably one of the best.

Tree Style Tab is an intuitive way to group your tabs into a visual route of your browsing. If you instead create new tabs each time you jump sites, you'll create a detailed 'tree' of how you found resources and where those resources took you.

The interface is fairly simple, but requires you to adjust where you look for your tabs. Due to Firefox's own self-imposed limitations, Tree Style Tabs can't hide the default tab bar and exists as a sidebar. You can still use the native tab bar, but you can create hassles for yourself by reordering tabs using the native tab bar rather than Tree Style Tab.

That said, Tree Style Tab can really change how you browse the web and task manage on the web. Also, you should probably pair it with an addon like Tab Unloader so you can unload tabs you're not using otherwise hundreds of tabs can bog down Firefox.