Firefox Disable Restore Session
By default Firefox loves to crash. By default Firefox will automatically restore your session after an automatic update, or when using the restart button from the Add-ons Manager. Firefox will offer to restore your session after a crash or other unexpected close.
Always restore sessions on start
Session Restore will restore connections to services which use session cookies to maintain login state, such as GMail.
Disable this.
Options > General > When Firefox starts > change from “Show my windows and tabs from last time” to anything else.
This does not work on crash and unexpected close situations, Firefox drags up the restore session window anyway.
Restoring a session once
Restore your session the next time you start Firefox, but not again.
about:config > browser.sessionstore.resume_session_once > true
Restoring a session after a crash
Restrict Firefox to automatically restore your session after one crash or unexpected close.
about:config > browser.sessionstore.max_resumed_crashes > 0
Disabling crash recovery
Disable the crash recovery feature, disabling crash recovery.
about:config > browser.sessionstore.resume_from_crash > false
This will prevent another user from restoring a previous session when Firefox is opened after a crash or other unexpected close, such as system shutdown while Firefox is running.
Completely disabling session store
Disable completely all session saving behavior, including the recording of session information.
about:config > browser.sessionstore.max_tabs_undo > 0
about:config > browser.sessionstore.max_windows_undo > 0
Sources
Mozilla Session Restore, applies to Firefox and SeaMonkey 2.
2012
"Firefox Disable Restore Session" describes how to prevent Firefox offering to restore your session after a crash or other unexpected close. Web Management.