Whenever you
1. Updated Firefox to a newer version
OR
2. Used this Step: Tools->Options->Security->Show Passwords->Remove All
OR
3. Pressed Ctrl+Shift+Del & then Had Selected "Saved Passwords" in that & pressed "Clear Private Data" button
I am sorry to say, but those cannot be recovered.

.Guys, Correct me if I am wrong.
I think from next time you need to use this addon for Firefox for Exporting/Importing your Saved Passwords:
Password Exporter
Chk this link for more info abt Password Exporter:
http://www.mydigitallife.info/2007/1...ird-and-flock/
Also, you know that in Firefox, anyone can view your saved passwords.
So set a Master Password for Viewing the Saved passwords.
You can do it like this:
Tools->Options->Security Tab ->Tick Use Master Password
Enter a Master Password & don't forget this password. If you forget this, then you are back to square one.