Any project on Glitch with a firebase.json file will display the deploy to Firebase controls.

To deploy to Firebase, click on the 'Deploy to Firebase' button shown at the top of the editor when viewing the firebase.json file.

If you haven't already logged-in, you'll be asked to do so, after which you'll be presented with a list of your Firebase Projects. If you haven't created one already, you'll need to go to Firebase and set one up. Then select which of your Firebase projects you'd like to link your Glitch project to, which will allow you to deploy from Glitch to the selected project on Firebase.

The deploy process will then begin, and takes just a few seconds. Once done, you can then select the 'View Firebase App' button to see your live project deployed to Firebase Hosting.