After installing xampp 126.96.36.199 in a new and clean Ubuntu 12.04 64bits, Firefox was unable to re-open with the last tabs. It always re-open on the default starting page. It worked fine before installing xampp.
I found the solution, thanks to askubuntu.com (http://askubuntu.com/questions/399891/problems-after-xampp-install-via-xampp-linux-1-8-3-2-installer-run)
Solution : You must completly erase Firefox history and its files !!!