It should have the permissions as set as in the OS install. At the OS install moment it should be created with standard options. If it’s there (default place) an you have not moved it for your session (set a new one in $FONTCONFIG_PATH) I don’t know why your PDF reader in your browser is claiming “Fontconfig error: Cannot load default config file” unless its reading permissions are denied. You can assure its readable by all with
chmod a+r /etc/fonts/fonts.conf
But I don’t really know if this is your problem here. It would be interesting to see the output of
ls -al /etc/fonts/fonts.conf
before adding the global reading capability using that chmod.