There is a bug when adding tabs also there popup UI makes it hard to mange. A new tab UI would be better to be able to see all at once comfortably.

Is the developer still working on this???

Hasn't been updated in 7+ months

Does not say if the history in each tab is also saved...

Pros :
- do the minimal job : save window tabs, add/delete tabs to groups/sets of tabs

Cons :
- doesn't automatically add new tabs to (or delete closed tabs from) a current/active group
- switching group open a new window -> if you switch groups 5 times between 3 different groups, you'll have 6 open windows (with duplicate ones)
- to add any open tab to any group, it is a 5-clicks operation (e.g. add the current tab to a group)
- on the "group view", one can expand the group to see the tabs, which is good, but the tabs are displayed with their URL, when tab name would be preferred
- cannot directly choose the tab you want to go when you switch group
- options that I didn't understand/see the purpose (Replace current Tabs and Active Compact Mode) as they seem to do nothing

I realy like the concept of this Add-On but, at this time, it doesn't allow me to add tabs to groups nor replace with current tabs. Also, if you could add bulk selection and handling of tabs it would be much more effective than, per example, having to delete every single tab.
It's a 5 star addon with those fixes! ;)

"replace with currently opened tabs" does not work

Need AUTOSAVE for open new tabs!

I hit a button and it just wiped out all the tabs I already had open. Looking further it's apparently designed to do that. Why? Why would anyone want that?

Reply to developer: It's okay. I wasn't doing anything important. Thankfully it's the weekend.

I would suggest users get the Chrome Store Foxified extension and install a copy of OneTab. OneTab is available as a Firefox addon but it's not up to date. Chrome Store Foxified is legacy, but you can disable or remove it after you get OneTab converted and signed. Hopefully OneTab's developers will port over their Chrome version because it works perfectly in Firefox.