After having removed some of my (many) tab groups, my problem with really bad performance was solved.

Yesterday I did the following:

  1. I started Firefox
  2. I right-clicked a tab and wanted to move it to another tab group
  3. after a short freeze/loading time, the list of all tab groups was accessible, and I selected one
  4. the tab moved away
  5. after that, boom!

I’m not sure what exactly happened, but I see the following symptoms:

  • Firefox is slow (closing a tab takes ~ 3-4 seconds)
  • (almost?) all my tab groups contain the very same tabs! (1-2 recently opened tabs and a few blank tabs)
  • So I can’t find my old tabs anywhere.
  • All my old tab groups seem to be there, but they all look empty (when opening one, I always get the same few tabs).
  • In the top right corner of Panorama there seems to be what looks like a few hundred tab groups, all stacked on top of one another. There seem to be all my tabs, and it looks like each one of them got its own tab group (?!). Trying to move one of these stacked tab groups takes around 20 seconds!

At some point after that always 4 Firefox windows opened. Two of them hadn’t any tab groups, the other two contained the (flawed) tab groups. When I tried to close one of the latter ones by clicking at the closing X icon, I got the warning message that this would close ~ 570 tabs (I don’t know my real tab number, but it could be that high, but it could also be the half of it; maybe the tabs got doubled somehow?). I closed the two "empty" windows without problems, after that only the 2 other ones opened when starting Firefox. Then I closed one of them too, confirming the warning message. Now I’m back at one window, which still contains the flawed tab groups and, what feels like, hundred of tabs (bad performance).

I tried to restore an older session, but unfortunately all backups seem to be empty:

Firefox profile: sessionstore.js backups are empty

I copied the only sessionstore.js containing content yesterday (a few hours after this whole accident happened), and there it had 4.3 MB. I tried to import this session into a new profile. All my bookmarks were successfully imported, but I had not a single tab group nor any open tabs.

What can I do?

My primary concern is getting all my tabs back, no matter in which way (a list of the URLs would to it, too). My secondary concern is getting all these tabs back into their tab groups.

I guess it could work by closing all those stacked tab groups, but that would take, like, days.


Okay, the problem is reproducible. Whenever I start Firefox now, this happens again.

The "solution" is to wait until the known Unresponsive script warning messages appear. As long as those messages don’t pop up, I can’t access any tab group.

Well, how to trigger these messages? Some time ago it was sufficient to load the tab group list (by right-clicking a tab and hovering over "Move to tab group"), but this doesn’t work anymore (because now it loads all tab groups but without the real tabs inside).

I found out that re-opening a closed tab seems to trigger the warning messages (right-click at tab bar). It doesn’t really open the last closed tab, though, as it seems to open a tab that was closed last in a certain tab group in the previous Firefox session (and not the tabs from the current session).

After re-opening one, two or sometimes three tabs the warning messages appear (until now, at least).

Then I click at "Continue" and after a few seconds all my tab groups are back to normal.

However, it seems that the "open last closed tab" function is broken for the whole session then. Even if you close a tab, the option is greyed-out.

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