There was a time not long ago when you used to have tons of Internet explorer windows and performed acrobatics with the Alt Tab to jump between different sites. Then came marvel called Tabbed browsing and yet the human's greed for innovation is insatiable. Presenting the Firefox Session Manager that lets you save a session and retrieve the session including tens of tabs you had open.
Session Manager Add-on that lets you do just that. You can save a current session and retrieve any crashes sessions. It also lets you name a session which means you can open tons of tabs and just save them. Great for eBay auctions when you are watching many items, or when you have many google search tabs !
Get the Add-on
But if Session Manager is too much and all you wanted was to save a session then Save session is for you. Get the Add-on
Also check out how you can Restart Firefox after enabling or disabling or changing a theme.