You are using Fx27 the Nightly.

I do not have that option on my Nightly but I do not know if it is a bug or if maybe they have deprecated this. IIRC there was talk of deprecating the tabsgroups.

P.S. Ooops, unthinkingly choosing a clean profile in Nightly was not a good test method !

Did you create at least one tab group by adding a name to a group?

The "Reset Firefox" function now preserves tabs and tab groups. So yes, my original 10 or so tab groups were migrated to the new profile Firefox made for me. I can enter the tab group "editor" and move pages among tabs as always, but that's a terribly inefficient technique. This is why the tab context menu item "move tab to group" function was so nice -- efficient, natural, to the point.

Hello. The "Reset Firefox" function is more humane than it used to be -- preserving tabs and tab groups. I'd probably used the same profile since Fx 4 beta days, so I thought it was time to give it a rest. And I do think Fx is better performing now with this fresh profile. But alas, there's this unexplained missing function. ;-)

That entry may be missing because the prefs aren't recovered.

• browser.panorama.experienced_first_run = true
• browser.panorama.session_restore_enabled_once = true

Outstanding, cor-el! I used about:config to add these prefs (after verifying that they weren't included in my set). I right clicked an entry, then used New -> Boolean to add both prefs. After a browser restart, the context menu item was back.

Do we have any idea why such a useful behavior is hidden by default? Maybe it's simply about hiding options "too complex" from the UI?

In any case, I thank you.

These prefs are set automatically when you create a first tab group by giving it a name.

Prefs aren't transferred when you reset Firefox, so maybe file a bug on this omission that fails to add these items to the right-click context menu when the prefs keep their default value, but tab groups were transferred.
I haven't checked if such a bug already exists.