Save Session is an extension for Firefox that will allow you to save the current session and restore them at the next startup.

With Save Session, you can choose to save the current session and close Firefox until the next startup. This works best if you want to launch Firefox with your default homepages with the previous session.

This extension is compatible with Firefox 2.0 and above. Download Save Session Extension from https://addons.mozilla.org/firefox/4199/.