3 years since the original post and as of 2.3.4 this issue persists. I ran into this yesterday and had to put my own DHCP server on the WAN to get that interface to DHCP an IP so that webConfigurator would even start.
I need webConfigurator to make changes to the WAN so it would actually connect to my ISP. Major catch 22 here. Why on earth would webConfigurator fail because it can't bind to the WAN IP of 0.0.0.0?. That's absurd. It should always bind to the (surely static) LAN address irrespective of what's going on with the WAN, up, down, misconfigured, or whatever.
I keep wanting to contribute to the project financially and recommend pfSense to clients but every time I turn around, there's a new bug that's years old in my exceptionally basic home setup.
For anyone else with this issue, you just need to be certain that your WAN gets an IP on startup, via whatever absurdity you have to pull in the shell to make it happen.