Generate self-signed certificate for Firefox to accept

I'm setting up an internal testing network, and I want FireFox to accept my self-signed certificates. Specifically, I'm trying to configure a certificate for nginx so I can use MyTestNetwork.dev and *.MyTestNetwork.dev.

Here is how I'm generating my certificates:

rm rootCA.* MyTestNetwork.dev.*

# Generate rootCA
openssl genrsa -out rootCA.key 4096
openssl req -x509 -new -subj="/C=US/ST=CA/O=MyTestNetwork/CN=MyTestNetwork.dev" -addext 'subjectAltName=DNS:MyTestNetwork.dev,DNS:*.MyTestNetwork.dev' -nodes -key rootCA.key -sha256 -days 365 -out rootCA.crt

# Generate Server Certificates
openssl genrsa -out MyTestNetwork.dev.key 2048
openssl req -new -sha256 -key MyTestNetwork.dev.key -subj="/C=US/ST=CA/O=MyTestNetwork/CN=*.MyTestNetwork.dev" -addext 'subjectAltName=DNS:MyTestNetwork.dev,DNS:*.MyTestNetwork.dev' -out MyTestNetwork.dev.csr
openssl x509 -req -in MyTestNetwork.dev.csr -CA rootCA.crt -CAkey rootCA.key -CAcreateserial -out MyTestNetwork.dev.crt -days 365 -sha256

And here is the SSL setup in nginx:

server {
    listen 443 ssl http2;
    listen [::]:443 ssl http2;

    ssl_certificate /etc/ssl/certs/MyTestNetwork.dev.crt;
    ssl_certificate_key /etc/ssl/certs/MyTestNetwork.dev.key;
    ssl_session_timeout 1d;
    ssl_session_cache shared:MozSSL:10m;  # about 40000 sessions
    ssl_session_tickets off;

    ssl_dhparam /etc/ssl/certs/dhparam;

    # intermediate configuration
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;
    ssl_prefer_server_ciphers off;

    # HSTS (ngx_http_headers_module is required) (63072000 seconds)
    # add_header Strict-Transport-Security "max-age=63072000" always;
    add_header Strict-Transport-Security "max-age=0;";

    # replace with the IP address of your resolver
    resolver 127.0.0.1;

    location / {
        proxy_pass http://$host$request_uri;
    }

}

There are two specific issues I'm facing:

1. Even when importing the rootCA.crt into FireFox via the "Import Certificates" setting in about:preferences#privacy, I get an error:

Websites prove their identity via certificates. Firefox does not trust this site because it uses a certificate that is not valid for dns.MyTestNetwork.dev.

Error code: SSL_ERROR_BAD_CERT_DOMAIN

Even though that I have the correct DNS record for that server (that domain hosts the dashboard for the DNS server I'm using).

2. I cannot curl MyTestNetwork.dev, as I get this error:

curl: (60) SSL: certificate subject name '*.MyTestNetwork.dev' does not match target host name 'MyTestNetwork.dev' More details here: https://curl.se/docs/sslcerts.html

curl failed to verify the legitimacy of the server and therefore could not establish a secure connection to it. To learn more about this situation and how to fix it, please visit the web page mentioned above.

Even though I create the certificate with the multiple SANs.

Any help is appreciated!