See also:

• [/questions/890425]

But why does my FF session disappear?

I don't know.

Do you mean that the Firefox window that was open with pages from that session is gone?

Did you close that window yourself or does it close on itself and is no longer open after resuming from sleep?

Or are you reopening Firefox and session restore doesn't restore the window with that session?

Do you mean that the Firefox window that was open with pages from that session is gone? YES

Did you close that window yourself (NO) or does it close on itself and is no longer open after resuming from sleep? YES. ITS LIKE I HAD QUIT FIREFOX BEFORE THE COMPUTER WENT TO SLEEP OR I HADN'T LEFT A FF WINDOW AND ITS TABS OPEN BEFORE I LEFT THE COMPUTER.

Or are you reopening Firefox and session restore doesn't restore the window with that session? NO. I USE THE "RESTORE PREVIOUS SESSION" OPTION FROM THE HISTORY MENU ITEM SUCCESSFULLY EACH TIME I COME BACK TO THE COMPUTER.

If you close the window before closing the Firefox application via Firefox > Quit then you won't get the session restored automatically.
To achieve that you need to close Firefox with that window still open.

Are you using this setting?

• Firefox > Preferences > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time"

If you close the window before closing the Firefox application via Firefox > Quit then you won't get the session restored automatically. I DIDN'T DO THIS. I DON'T KNOW WHY YOU THOUGHT I DID. THERE HAS BEEN NO AUTOMATIC RESTORATION UPON RESTARTING FF AT ANY TIME.

Are you using this setting?

   Firefox > Preferences > General > Startup: "When Firefox Starts": "Show my windows and tabs from last time" 

I DIDN'T KNOW I HAD TO DO THIS.