I solve the trouble! I get libstdc++*.* from a Mandriva 2006 that I use at home, tar them transmit to here in my job, where I use Fedora Core 5. Then I untar them in the local /usr/lib.
Imediatelly Mozilla Firefox begin to run normally.
But I get a new trouble. I can't put a shortcut in the desktop. I tried to create a symbolic link in the Desktop but when I double click it, linux ask me if I want to execute or edit or...
When I choose execute, it opens a konsole window and runs Firefox OK, but, obviously, I can't close the konsole window.
Hey mr. Ken! If you want a copy of the tar.ga file that solves my trouble, please send an e-mail to email@example.com
and I'll transmit it to you.
P.S.: Thank you guys!