Firefox takes a long time to resolve first website, but is fine after that

We are using firefox on Redhat 7 workstations and, when we first open firefox and attempt to load a web address it takes 25-30 seconds to connect. After that first attempt, web addresses load almost instantly. Our systems are only connected to a local network and not the internet, if that makes a difference. Also, we are using web addresses and not IP addresses. When I try by Ip address it's much faster, but I get the security risk warning for the ssl cert. So I'm not sure if my issue is something between firefox and dns, or if it has to do with the SSL certs? Both dns and ssl are handled by Red Hat IDM. We are seeing the same behavior on all of our workstations.