This might be known to many, but to those who do not – this might be helpful.
We like to back-up important data when we perform a fresh installation of any OS. However for those who deal with a large number of tabs in their web-browser, all these tabs amount to useful information (browsing history, bookmarks, tab-groups, etc.) which we would not want to lose with any fresh installation. Being able to restore all this information on a fresh Firefox installation is certainly welcome.
Today I freshly installed Fedora 18 with KDE to upgrade from Fedora 16. So while backing up my data I copied the ~/.mozilla directory as well. This directory has information related to all browsing sessions. After installation of Fedora 18, I just went to my home directory and copied back the .mozilla directory from my backed up data to ~. Running firefox -p then allows you to select from the browsing profiles, and you get back all your tabs, tab-groups, browsing history, bookmarks, etc from your previous sessions. Result: No information lost. :)
Cheers and happy browsing!