Just installed it and Wow! It is reacting to clicks much faster than Tree Style Tabs. Does not seem to require too broad permissions. Does not come with attempt to show tabs in tree which I anyway disabled whenever I could. Just seems to do well what it should do.
I hope that Firefox stops leaking memory like crazy as it used to do with TST.

I wish it also had bright color theme with less intense colors.

Not really a review, just a question on the add on. Is it possible to move the vertical tabs to the opposite side of the screen?

I like the clean look and it works well for most part, like it has reload all tabs built-in, but it can't select group of tabs to bookmark, the original tab bar in firefox or tree style tabs can, yes u can bookmark all tabs but no selective, I hate the horizontal tabs bar on top, make my neck hurt to look up and down the tabs, my favorite is at bottom of window, but settle on the side with no choice.

I just started using VTR today and find it clean, unobtrusive and easy to use and works well with the native Firefox sidebar. I think it will become my fave tabs manager very quickly.

I use macOS Catalina 10.15.4 and I can't hide horizontal tabs; without this feature the extension is much less useful.

FOUND A BUG! Devs please fix this as this is really annoying! When I open new tab and close it, it does not activate THE PREVIOUS tab, but rather next tab below the one closed! Imagine I google something and keep opening and closing results in new tabs. All the time I need to manually switch back to my google results. Very frustrating.

The latest version no longer allows me to simply cycle through my tabs. Instead, a very limited switcher appears. Very, very annoying. And switching back to the previous tab with shift+tab now opens a menu of tabs instead. That's a deal-breaker. I'm removing this annoyance, and looking for a solution that isn't trying to be so 'cool', or trying to be too much more than just a way of listing my tabs on the right. Why did you do this to me?

Works very well. Not sure if it is possible, but it would be nice if windows with only one tab hid the sidebar by default.
update: does not work in Android on my Cosmo Communicator. nothing is visible.

Ookoo...

For every one looking for a solution to hide the horizontal tabs, tested and approved : https://www.hackerway.ch/2017/11/17/firefox-57-quantum-and-vertical-tabs/

I was using Tab Kit 2nd Edition and very much liked it. With Version 52.0 it went obsolete, so I'm using this now, This is pretty nice, but a couple of things I'd like to see:

1. Resolution to hiding the horizontal tab bar.

2. A true autohide of the vertical tab bar that does not require Ctrl-Shift-V.

This is very nice anyway. Would be great to see these things as well.

Fellow dev here. Nice work - this is great.