Firebase Hosting can connect to your own custom custom domains, like
https://myrealtimeapp.example.com. Firebase Hosting provisions an SSL certificate for your domain and serves
your content over a global CDN.
Verify domain ownership
Before connecting a custom domain, you'll need to click through the "Get Started" wizard in the Firebase Hosting admin panel. This is where you'll be able to see a history of deploys and manage connected domains.
From the Hosting panel of the Firebase Console for your project, select Connect Domain.
Enter the domain that you would like to use in the input and then select Continue. This will validate your domain hasn't already been linked with a Firebase project. If you would like to redirect all requests on this domain to another, you can select Redirect requests on this domain to another domain and enter the domain you wish users to be forwarded to.
In most cases you can use Quick Setup. Point the DNS A records for your domain to Firebase Hosting, and an SSL certificate will be automatically provisioned within a few hours.
If you already have a site running on another hosting provider and need a zero-downtime migration, you should choose Advanced Setup from the dropdown. You will need to either update your domain's TXT records or upload a file to a specific location on your existing site to verify your domain. Once verification is complete, you can safely point your DNS A records at Firebase Hosting.
Wait for SSL certificate provisioning
Once domain ownership is verified we will provision an SSL certificate for your domain and deploy it across our global CDN. This process can take several hours.
Domains will be listed as Subject Alternative Names in the FirebaseApp SSL certificate.