DNS Forwarder not responding to internal requests

I have a server 2008 R2-level internal domain protected by a pfSense firewall. The firewall is set up as a DNS forwarder, and it has no problem resolving queries from its own web interface (using dnslookup). My internal DC is setup to handle AD, DNS, and DHCP. Everything works fine internally - names resolve, IP addresses are issued, etc.
However, I began getting complaints that users could not reach hotmail.com, outlook,com, or live.com - or any of their subsites.
So, I began troubleshooting, and it appears that the names are not resolving internally. The DNS request flow is basically :

client -> internal DNS -> firewall (DNS forwarder) -> ISP

I was able to get the addresses to resolve about 50% of the time by adding the ISP DNS to the DNS forwarders on the internal DNS server, but I understand this is a bad practice, as it could expose AD.

So my question is:
Does anyone know why pfsense would just refuse to forward DNS requests? The dnsmasq service is running and (appears to be) is listening on the internal LAN IP. IF is run wireshark, what should I be looking for to tell me where this is going wrong?

Or is there some other basic issue that I haven't thought about yet?