If you want to reduce your costs, you can have HTTPS with a custom domain on a free Heroku app by using Cloudflare. Why are you using Firebase to serve quotes? I imagine the dataset could number just a couple thousand quotes max, which is fine to serve from memory after loading from a file at startup.

Or if you're using Firebase as a convenient interface for adding new quotes, the app could update its internal cache of quotes once a day, without having to pay Firebase for each API call.