Session Manager Firefox Add-on is a an extension that allows users to save their current session and then restore it later. It does exactly like what it calms, saving all Firefox tabs and windows so that you can access them later the way they were.
Once installed, it will add Session Manager option in the Tools menu from where you can Save, Restore, Remove, Organize, and Edit Sessions.
Once you Save the session, you will be asked to give it any custom name. You can also add them to a group for better organizing your sessions.
Organizing sessions can be useful if you want to visit few selected websites daily. Instead of selecting them from bookmarks or typing the name manually, you can just restore a session from the group and all websites will load instantly.
Note: If you are a non-Firefox user and want to load multiple websites in a single click, read this guide.
The Sessions that are not added in Groups are listed directly in Session Manager menu for quick access.
For a complete guide, make sure you have read the official documentation which will open after you have installed the add-on.
It works on Firefox 3.0, Firefox 3.5, and all latest releases. The developer updates the add-on frequently. Enjoy!