Not much you can do afterward unless you find a session.js or session.bak from when you were okay. If you find one then make a copy of it so it doesn't get destroyed.

I had made a suggestion to look through History to find them, but I expected History to show up each time you start up Firefox and that does not happen for app-tabs they are already open.

If is very important to close Firefox properly through File -> Exit (or the red button) and not to use the [X] in the upper right corner that closes a window.

Make sure you save your browsing history, and that you won't clear it at end of session or accidentally through the Tools > clear history

• http://img232.imageshack.us/img232/4928/clearcachew.png

There's hardly a day where I don't destroy my app-tabs and I bookmarked them from the very beginning in a folder simply because I figured they would get lost or damaged sooner or later, never expected to be each day though. but they do last through to the next session. I load them up from a bookmark folder after I've damaged 2 or more and don't have text areas with work in progress, and use the "Multiple Tab Handler" extension to pin selected tabs all at once. The only problem with bookmarking is that the have to be immune from sorting so have to have sortable titles, or lots of bookmark separators just so they load up in the correct order.

Some references:

• How to restore Lost App Tabs and Tab Groups | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/861318
• when I click on a link, Firefox opens a new window for that link, how do I change this setting? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/861194
• Editing an answer | have tried the various suggestions in Lost Bookmarks but they still get lost | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/861297/edit/230257
• After downloading Firefox 4, my Google Toolbar disappeared. The new F4 page has no View, Tools etc at the top. WHY would I risk this again by accepting the invitation to download 5?? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/860628
• D- Tab Capacity Test
  file:///c:/copiedsite/dmcritchie/firefox/tab_capacity/toplevel/d.htm
• E- Tab Capacity Test
  file:///c:/copiedsite/dmcritchie/firefox/tab_capacity/toplevel/e.htm
• Search | Firefox Help
  https://support.mozilla.com/en-US/search?a=2&a=1&num_voted=0&updated=0&created=0&page=2&q=Session_Restore+app-tabs&sortby=0&w=2&is_solved=1
• My websites that are pinned as apptabs don't restart the next session | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/858098?s=Session_Restore+app-tabs&as=s
• restore previous session is not available | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/855008?s=Session_Restore+app-tabs&as=s
• how do I **save** tab groups (or import/export them)? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/849739?s=Session_Restore+app-tabs&as=s
• I used to have "app tabs" & now it's gone. I recently updated Firefox & I also changed the skin. What can you suggest to me? | Firefox Support Forum | Firefox Help
  https://support.mozilla.com/en-US/questions/844668?s=Session_Restore+app-tabs&as=s

Cor-el has tips on working with app-tabs by saving a Session Restore, I think has something better that what I included above.

App tabs don't copy to new windows. In addition, app tabs are only remembered if they are in the last window closed. Together, this forms a bug of lost app tabs. Now where can I find the developer's contact info?

App tabs are connected to a specific window and opening a new windows doesn't inherit (App) tabs from that parent window.

You need to use "File > Exit Firefox" to close all open windows and the Firefox program to reopen them all the next time.
Otherwise you only close the current window and only the last closed window is saved via session restore.
Closed windows are probably still recoverable via History > Recently Closed Windows.

As well as having had this problem a couple of times on different machines, both immediately after upgrades, I also use the synch capability so that tab groups from more than one machine can be accessed from any of the others - a really useful capability. It's really frustrating to have lost everything and have to try to recreate things from history. It occurs to me that the contents of my sets of groups are stored on a synch server somewhere so they ought to be recoverable from the hopefully, periodic automatic server backups - only problem is, how to access them? unlikely to be possible at this stage!

In this context, a useful enhancement would be a capability to make user-created named backups of all current groups of tabs which could later be restored at will; any upgrade process should also automatically create such a backup for the user so that the problem of lost groups of tabs would be solved. In addition it would give users additional flexibility to create groups of groups - accessed by the save/restore mechanism - say for development, personal or social or whatever.