Some people have reported a problem seeing or getting to the guestmap with firewalls or popup blockers enabled. Any solution to this?

Turn off the blocker.

Unfortunately, I have no control over my guests' choice of software. You are saying then, that the guestmap will not work if visitors have a firewall enabled?

I am saying that if a visitor has popups blocked, or a firewall that disallows some html or javascript from being rendered, then yes, the guestmap may be affected. The guestmap is a very basic script so the chances of it being blocked are pretty small.