failed to start daemon: Error initializing network controller: Error creating default "bridge" network

Found out that

$ firewall-cmd --get-active-zones
FedoraWorkstation
  interfaces: ens4u1u2 wlp59s0
docker
  interfaces: br-48d7d996793a
libvirt
  interfaces: virbr0
trusted
  interfaces: docker0

the interface docker0 seems to be in the trusted zone. But there's another zone called docker.

So I decided to give it a shot and add it to the docker zone instead.

$ sudo firewall-cmd --zone=docker --change-interface=docker0

Looks like this afterwards:

$ firewall-cmd --get-active-zones
FedoraWorkstation
  interfaces: ens4u1u2 wlp59s0
docker
  interfaces: br-48d7d996793a docker0
libvirt
  interfaces: virbr0

Seems to work.
Maybe someone can shed more light on this.

I got this error after upgrading docker-ce on my Fedora 32. It looks like the new docker conflicts with the manual firewall configuration mentioned in the article you linked in your answer. I had the rules on my machine to enable container-to-container communication.

Docker started successfully after I reverted the firewall rules:

sudo firewall-cmd --permanent --zone=trusted --remove-interface=docker0
sudo firewall-cmd --permanent --zone=FedoraWorkstation --remove-masquerade
sudo firewall-cmd --reload
sudo systemctl restart docker

The changes don't seem to affect the ability of containers to talk to each other.