I own a domain through GoDaddy with the .app extension (call it mydomain.app). I have a site hosted on Firebase Hosting for this domain and it works fine. However, the website only loads through https://mydomain.app and not https://www.mydomain.app. I have the DNS properly configured according to GoDaddy tech support and wonder if I'm supposed to explicitly add www.mydomain.app in Firebase hosting in addition to mydomain.app? Seems redundant. Or is this not necessary and I have a configuration problem on my hands?
Go to GoDaddy, where you added your A record to point to Firebase the first time.
Since it's working, that means you configured it to use
@ ==> your FirebaseAppUrl.
Under it, now, add also another A record, to configure your www.mydomain.com,
by adding www A record, to point to the same place.
www ==> your FirebaseAppUrl.
Keep both records of course in GoDaddy.