Can Sesame be run behind a firewall?

Yes. Sesame can be set up so that only computers behind the firewall can gain access to the Sesame server. With most firewalls, this will be the default (and desired) behavior. See your firewall's user manual for details on how to allow a program to operate through the firewall, if you want to make your Sesame server available to the public. Some firewalls will produce a warning when Sesame is first launched indicating that a program has "opened ports". Your firewall may need to be informed that Sesame is going to open two ports. Again see your firewall's user manual for details.