The restore session feature of Firefox is very nice to have. Firefox 2.0 will attempt to restore a session connection if the browser dies. However this has security implications especially for banking or any service with a login. See below for Mozilla Foundation notes:
The Session Restore functionality provided in Firefox 2 will restore connections to services which use session cookies to maintain login state such as GMail. It is recommended that users with concerns about the privacy implications of this behavior change the value of browser.sessionstore.resume_from_crash to false.