Install Firefox if you don't have it, this tip require Firefox to be present (dugh...!!
www.getfirefox.com
Open Firefox
Go to Tools choose Options
on Main tab look at Startup section
there is a Combo box option which says “When Firefox starts”
select “Show my Windows and Tabs from the Last time”
Now if you browsing with many tabs, close them.
Open Firefox again, then all tabs you open before you close Firefox will be restored.
I think Firefox dev. team adding these feature because it should a standard feature not an addons.
Anyway, I am using it since my SessionSaver plugin not able to run when I am upgrading my Firefox into version 2