I can't click on the Firewall tab
I've just discovered that I can't access the Firewall tab in the Security & Privacy settings pane. I click on it, but nothing happens. I'm pretty sure that I was able to do this before and turn my firewall on - I get asked sometimes if I can allow an app to receive incoming connections.
MacBook Pro (15-inch 2.4/2.2 GHz), Mac OS X (10.7.4)