The feature is implemented as an XPCOM service. (Note: Firefox exposes this preference in the Startup section of the Main pane of the Options/Preferences dialog.)

(int) - What is displayed when Browser starts: 0 = blank page 1 = homepage 3 = previous session.

This is used for restarting the browser after application updates and extension installation.

_session_once (bool) - Resume session at the next application start, but not again.

_from_crash (bool) - Resume sessions post-crash.

So the user is asked after the second crash which pages he wants to restore.

_resumed_crashes (integer) - Number of crashes that can occur before the about:sessionrestore page is displayed.

(integer) - minimal interval between saving operations in milliseconds.

Valid for Firefox 2 and 3, superseded since Version 3.5. May not appear in about:config until changed. See the source for currently available settings and their default values. The default settings will restore the session after a crash and previous history will be restored to a certain point.

Prompt for restore upon application start, post-crash.

Allow the user to 'undo' closing a tab or window (P2).

If post-crash, allow the user to choose whether to restore (P1).

Automatically restore the session data upon restarting from a forced closure (P1).

The API will provide a stable and intuitive base which power-user oriented extensions, or expanded features in future releases, can build upon. This minimal implementation provides an unobtrusive user-experience while meeting the broadest use-cases. The feature will be passive, reacting only to forced-restarts such as extension installation and crashes.

The state of various window, tab and user-data will be saved, and reloaded upon application start. After a forced restart, restore the user's workspace exactly as it was.

Firefox browser history location