App (pinned) tabs and Tab Groups (Panorama) are stored as part of the session data in the file sessionstore.js in the Firefox profile folder.

• http://kb.mozillazine.org/Profile_folder_-_Firefox Firefox
• http://kb.mozillazine.org/sessionstore.js
• http://kb.mozillazine.org/Session_Restore

Make sure that you do not use Delete browsing, search and download history on Firefox to clear the "Browsing History" when Firefox is closed because that prevails and prevents Firefox from opening tabs from the previous session.

FF4.x has so many bugs, I have to Clear Recent History to clear "Browsing History" every time I shut down. Losing all my app tabs and all of Panorama has not been a problem before today.

I have a similar problem, but I accidentally clicked start new session instead of restore session, and it erased the tabs...

If you have Firefox 4 and haven't closed Firefox yet then you can try to restore the previous session via "History > Restore Previous Session". That will make Firefox load the session stored in sessionstore.bak

I have figured out this annoying glitch and it's weird to reproduce, but I have.

On a MAC you have two options to quit. One is to use Firefox/Quit in the top menu bar. The other is to use the Mac menu Firefox icon in the Menu bar at the bottom. Right click/Quit.

HOWEVER, before you try this - the app tabs ONLY disappear WHEN you close the Firefox window first (top left X) THEN use right click/QUIT on the menu bar.

If the Firefox window is open when you right click/quit, the App Tabs remain.

Hope Mozilla read this.

If you close all Firefox windows on Mac then the Firefox application is still running (you have the Menu bar and can open a new window in that same session).
You need to keep at least one window open with App Tabs and quit Firefox via "Firefox > Quit" if you want session restore to restore those App Tabs and possibly other tabs from the previous session.
Only windows that are open at the time that you use Firefox > Quit will be restored.
So this is not a bug, but caused by misunderstanding how closing windows work in relation to session restore.

It is the same on other platform if you use the close X to close a window thinking that it is the only open window and then notice a forgotten pop-up window that you had missed. If you do not restore that closed window then session restore will only open that last closed window. You always need to use Firefox > Quit/Exit to close the Firefox program with all open windows to avoid such surprises.

This needs to get fixed. I also noticed my bookmarks have been violated. I had a Gmail bookmark that disappeared.

All opened windows need the app tab info within, even if FF doesn't show th app tab. Have a setting that allows "show app tabs in alternate windows"

FF5 W7

FINALLY! I kept getting old tabs I didn't want, even after Quitting Firefox. I used the suggested technique of clicking the red X box first, then the Firefox icon in the Dock, or lower Menu Bar as he calls it, and when I reopened, I was mercifully free!