I would like to have different firewall rules for different WiFi networks. Is this possible with the default Windows 8 firewall?
There is only one way, and surely not what you are looking for. Windows firewall can only have different rulesets for different network profiles (domain, private and public), so your only chance is to configure one WiFi network as public and the other as private, and create different firewall rules for every profile, but keep in mind that this will affect all other networks which share profile with them.
Achieving exactly what you (and me) would like to achieve needs third party software.