As an IT technician, I'm often switching between multiple tabs.
This add-on allows me to group tabs according to my customers, and simplify my day-to-day navigation.
A very useful feature of this addon is the ability to associate a group with a tab container: cookies are compartmentalized, so I can easily use several admin accounts on the same admin portal at the same time (several admin 365 accounts...).

Very powerful, easy to use, convenient. Great design!

Very useful for organizing my tab hoarding habit

[3 September 2024 Update]: Great Addon but since I installed it, it conflicts with the 'Tab Session manager', and causes errors to my Firefox. Please fix that problem].

WOW! Thanks to this video on YouTube (How to Use Tab Groups in Firefox) BY "The Linux Cast
"channel. That has demonstrated this extension, and I am glad I found that video. Because this Add-on is Truly helpful and convenient to me. Because I have 3500 tabs open in my browser and it makes my life much easier now that I have them in groups! Thank you for creating such an awesome extension!! 🌟🌟🌟🌟🌟👍

The best tab management plugin I've ever found. Easy to move tabs into different groups, and best of all, you can have many, many different groups without slowing the browser down because they are only loaded when necessary.

As a recent Chrome uBlock Origin refugee, I was looking for something that'd replace chrome's tab groups.
This add-on does a little bit of that, but differently, and in several ways better.
First off, you WILL want to customize your browser toolbar to put the add-on icon to the top left of the app, right before the tabs. It's a much more natural place to use it.
Second, if you're using dark mode, the default icon is hard to see, and you'll have to tweak a config to fix that. It's spelled out in the "about this extension" page.
Third, if you multi-screen, this is MUCH better than chrome tab groups, since it allows you to trivially move tab groups between windows, and therefore screens.
I like that it can sync the tab groups into a bookmark folder.
The default group icons are awkward, but you can replace them with the favicon of any tab within the group, which solves that.
I just installed this a couple hours ago so I'm still wrapping my head around it, but I like it already.
I've got 12 tab groups already. Just don't expect it to be a drop-in replacement for Chrome tab groups. Take the time to wrap your head around the mental model of this add-on, it's worth it.

*Edit, now with more gripes!:
A dozen tabs or so (about 8% of my tabs) get detached from their group on every Firefox restart, which means on every Firefox update for me. I don't know why. It's not the same tabs each time. I tweaked all the settings I could, didn't help. I have to reassign the stray tabs in their proper groups after a restart, which takes entire seconds.
I'm kinda hoping this is going to stop happening on a future update. If I was a little less lazy, I'd probably try to debug it myself.

Essential plugin. Way better than Chrome tab groups. Does everything I need