A good attempt at this sorely needed feature set, but not quite there.
I was particularly excited about the Slim bar with hover, but unfortunately this feature simply does not work properly; though the content in the side bar does indeed extend, the bar itself does not, rendering this feature unusable.
Another big issue is the inability to drag tabs out into new windows, or onto other existing windows, another feature I was depending on.
For these reasons, I cannot recommend this add-on in it's current state, but I am hopeful it will be fit for purpose in the future.

Downloaded exclusively to hide the horizontal tabs and followed the guide to a tee. However, this did not work for Firefox 130.0

Very disappointed

Splendid add-on! Switched back to FF from Edge when found out about Sidetabs, been using it for half a year or so, and it just delivers on its promises. Thank you!
I only wish tab grouping also came with this thing, but it's good nevertheless.

Looks like what I needed! but it does take away some built-in functionalities..
Like exchanging tabs, aka the ability to drag tabs "out" to a new or different window.
Right click -> close tabs below\above.
Drag text, links or other "objects" into or beside existing tabs to open new (or that existing) tab and search the item for ex.
In short, it doesn't act like FireFox's default tab system yet.
It also collides with other tabs that happen to reside on the same side like the history tab.
While I did gained more real-estate, my productivity were impacted..

Very good would be perfect if have option to group tabs

Lack of a narrow sidebar like Brave is the one thing that's been holding me back from coming back to Firefox.

Love it, thank you!

Breaks every time you restart the browser, forcing me to reinstall the extension to fix it. Not sure if it's just me, but had no such issues with Sideberry.

Integrates well with themes, the expand sidebar on hover doesn't work for me (librewolf-firedragon). It would be good to have an option of 'alternative colors' in rows to see multiple tabs more clearly.

Absolutely love this extension. I also love the support for using it with userChrome.css as this has really made my vertical experience with Firefox much nicer.

With this extension and the sliding alternative in userChrome.css I really, finally, feel like the browser is out of the way of using it.

Looks and functions the closest to vertical tabs on Microsoft Edge in my opinion among the other add-ons I have tried so far like Sideberry, TreeStyleTabs. One thing I would like to see is an option to make the tabs' icons/title bigger so that it could be easier to click on.

A good straight-forward simple extension for vertical tabs without bloat. Two features I'd like to see: (1) Double click to close tabs (important for Mac laptop users as middle click is not available on trackpad) and (2) Respect Simple Tab Groups tab groupings and display only tabs for the active group. Many other vertical tab extensions can do this.

This is exactly what I wanted for vertical tabs. Clean UI, matches my firefox theme, and it just works. I really like the copy-paste user chrome as well.

Really appreciate the inclusion of very straightforward and simple guide for CSS customization :) It finally looks clean enough for me to daily-drive vertical tabs

This is the extension that really feels like a native sidebar. It works great with themes. The design is simple but powerful.

Beautiful UI! Better pinned tab without text and add tabsearch