Aggressive firewall preventing Apache connections

I have the Mac firewall on and it is causing pain for web sharing.

So I have the firewall on (system preferences, security, firewall, "on") and I have web sharing on (system preferences, sharing, Web Sharing, box ticked). I can view my website from my computer, but not from other computers on my network. If I turn the firewall off, I can then see it and web sharing works great. In the firewall "advanced" dialogue I have only stealth mode checked and "Web Sharing" appears at the top with a green circle next to it.

I should also mention that it is certainly possible that I modified some config file under a previous OS X version.

here is a typical console line

Jul 6 21:08:23 macbook Firewall[69]: Deny httpd connecting from 192.168.1.138:3580 to port 80 proto=6

Argh! I wanted that connection to work!