Restarting computers will result in having to sign back in and if autosave is set you still have to confirm the correct login for the site. As to the trust this PC this is something financial or Government login always request you to do regardless this is their security measure. This isn't something the Browser can change AutoFill doesn't mean auto-login the user must still select the correct Autosaved login to login to the site and Secure sites will always require you to "Trust this PC" every-time. So this isn't a Firefox issue as that's how it works.