--- 
networks: 
  firefly_iii_net: 
    driver: bridge
services: 
  firefly_iii_app: 
    environment: 
      - FF_DB_HOST=firefly_iii_db
      - FF_DB_NAME=firefly_db
      - FF_DB_USER=firefly_db
      - FF_DB_PASSWORD=firefly_db_secret
      - FF_APP_KEY=S0m3R@nd0mStr1ngOf32Ch@rsEx@ctly
      - FF_APP_ENV=local
      - TZ=Europe/Amsterdam
    image: jc5x/firefly-iii:develop
    links: 
      - firefly_iii_db
    networks: 
      - firefly_iii_net
    ports: 
      - "80:80"
    volumes: 
      - 
        source: firefly_iii_export
        target: /var/www/firefly-iii/storage/export
        type: volume
      - 
        source: firefly_iii_upload
        target: /var/www/firefly-iii/storage/upload
        type: volume
  firefly_iii_db: 
    environment: 
      - MYSQL_DATABASE=firefly_db
      - MYSQL_USER=firefly_db
      - MYSQL_PASSWORD=firefly_db_secret
      - MYSQL_RANDOM_ROOT_PASSWORD=yes
    image: "mariadb:latest"
    networks: 
      - firefly_iii_net
    volumes: 
      - "firefly_iii_db:/var/lib/mysql"
version: "3.2"
volumes: 
  firefly_iii_db: ~
  firefly_iii_export: ~
  firefly_iii_upload: ~

--- 
networks: 
  firefly_iii_net: 
    driver: bridge
services: 
  firefly_iii_app: 
    environment: 
      - FF_DB_HOST=firefly_iii_db
      - FF_DB_NAME=firefly
      - FF_DB_USER=firefly
      - FF_DB_PASSWORD=firefly
      - FF_APP_KEY=S0m3R@nd0mStr1ngOf32Ch@rsEx@ctly
      - FF_APP_ENV=local
      - FF_DB_CONNECTION=pgsql
      - TZ=Europe/Amsterdam
      - APP_LOG_LEVEL=debug
    image: jc5x/firefly-iii:develop
    links: 
      - firefly_iii_db
    networks: 
      - firefly_iii_net
    ports: 
      - "80:80"
    volumes: 
      - 
        source: firefly_iii_export
        target: /var/www/firefly-iii/storage/export
        type: volume
      - 
        source: firefly_iii_upload
        target: /var/www/firefly-iii/storage/upload
        type: volume
  firefly_iii_db: 
    environment: 
      - POSTGRES_PASSWORD=firefly
      - POSTGRES_USER=firefly
    image: "postgres:latest"
    networks: 
      - firefly_iii_net
    volumes: 
      - "firefly_iii_db:/var/lib/postgresql/data"
version: "3.2"
volumes: 
  firefly_iii_db: ~
  firefly_iii_export: ~
  firefly_iii_upload: ~

Update docker file to match postgres.
Update docker file to match postgres.
