It seems that the Mozilla package you are trying to install is compiled against a wrong version of glibc (which is the GNU C Library). You should probably only use the official Fedora glibc RPMs if you are not sure what you are doing, as otherwise many programs could become broken because a lot of stuff depends on glibc.
Getting a new version of Mozilla by other means seems a good solution. Besides downloading it from
their web site, you could try getting an (unofficial) RPM from here:
http://dag.wieers.com/home-made/apt/packages.php
I don't know how VLC uses Mozilla or why it needs a certain version of it. So if you install it somewhere else than what the default is in Fedora, you might have to do some adjusting.
Regards
Simon