Very promising Tab Groups successor.
Edit:
After 3 years this had become one of the most irreplaceable must-have extensions for me, and I have to commend the developer for still maintaining it. I'm still baffled why such useful functionality (Panorama) was removed from FF in the first place.

This is a great addon, but I'm sticking with an older version because the current version gives it permission to "Access your data for all websites".

I realize that this permission is being used to create site thumbnails, but would it be possible to create a version that doesn't include thumbnails so that such a broad level of access isn't required?

FINALLY A PLUGIN REALLY THAT WORKS!!! As a web developer, I have like a million tabs open at the same time and this feature is a MUST HAVE to allow me to group tabs! (I started grouping tabs before Firefox added the feature, so I move to firefox feature, then they removed it and I started using a plugin but It stopped working .. was missing this feature untill now)

This is a terrific, must-have add-on for researchers and people with busy, creative lives. As a researcher, graphic designer and IT professional, I am often involved in dozens of projects at once and it's not unusual to have dozens of tabs (often several dozens) for each project. This add-on allows me to segregate them into logical groups and call up and use just the group I need, organized the way I want.

In locating parts and ideas for building a custom PC for a client, for example, I may open and use dozens of tabs; with this add-on, I can keep them all grouped under the client's name and share them with the client.

I work with Adobe Illustrator a lot; with this add-on, I can organize the pages, tutorials, online graphic resources, etc., in logical groups, available at the click of an icon. These are just a couple of examples; I have over 25 such groups right now.

I was using Tab Groups by quicksaver (a thousand thanks to you, my friend!) and actually stopped upgrading Firefox at v54 so that I could keep using this essential (for me) functionality. Glad to finally find a worthy successor to that add-on so I can keep working the most efficient way for me! I can hardly recommend this add-on highly enough!

Really great to see this extension, but please please allow the user to select whether or not tabs are closed in the current group when switching to a new group. I would even suggest to make it the default to keep all tabs open when switching since the current system of closing tabs will cause more headache, confusion, and mistakes from your users than any benefit like a lower memory footprint would make up for. It takes 5 seconds to close and re-open FF if you're looking to free up resources.

Great working app. Works fine and provides the missing functionality after the recent switch of app functionality. Great that it also describes the reasons for the required permissions. Still would like to see that 'Access your data for all websites' requirement is removed, this permission just for favicons seems a bit overkill.

im totaly excited having this add-on. it just does what i need. stable, nice, easy to use. i followed the dev from the first day, it had had all of those bugs, growing to a "version" i trust in for my daily shit i want to do with it. thanks guys .. realy appreciate what you've done so far. thanks! happy to support were ever i can...
for the negative comment from jonnoN some days ago:
"Unloads tabs that are not in the active group. Want to listen to music? Too bad! Useless."
--> mate, just pin the tab you want to listen to and it stays active. ... don't rate it bad for that, please

Working good so far. Good replacement. Any chance that at sometime in the future tabs opened in one group will stay open when you switch to another group like they did in pre-Quantum extensions?

Would be better to use tabs.hide() from firefox 59.

I do love this add-on. However, if you are adding this to an already used window with multiple tabs, you should make sure to add ALL current tabs to new groups BEFORE you attempt to switch to a new group. I lost a few hundred tabs and using History, spent two weeks trying to re-find those lost tabs. A good idea for multiple tabs would be an add-on similar to "Copy All Tabs Urls WE" 1.0.4 By Michele Pezza - at least you won't lose your tab's addresses.

Awesome! I was missing Tab Groups.

Awesome!

Would be great if you could add the option to show the group NAME I am in at the moment.

PS
Please also consider to use the Awesomebar special charakters (%,~,#,..) in your search field!
PPS
Invalid tab ID: 788 appears more and more often! Please fix it! We are losing tabs!

I missed old Tab Grups :)

Like bellow, quick change groups is difficult. add-on have a slow response.

Add seems to have a bug, if last tab is a new empty tab is selected, impossible to switch btw groups.

i need to clic another tab to have the possibility to switch.

Other things. Is it possible to add option to don't reload the active tab?
When filters on a site are activated, all is reset like a new visit.

1 star and it's perfect

Tab Group reborn (almost)

Step by step I retrieve "Tab Groups" module's features.
Very useful module, thanks!

needs to be better. not functional enough.

Almost there. I loved the free arrange of groups on the prior version; but I understand it is coming in the future. Best Tab grouping out there, bar none. Easy to see icons, great graphical interface, easy to export. In fact, the reason I delayed updating to the latest Firefox was because Tab Groups was not in place. Now it is.