Set firebase authentication in postman

Setup a POST => request;

Replace firebase api key in the url => "https://www.googleapis.com/identitytoolkit/v3/relyingparty/verifyPassword?key={FIREBASE_API_KEY}"

Pass the following params in the body of the request 
{
    "email": "<email>",
    "password": "<password>",
    "returnSecureToken": true
}

To create an automated setting of this token, you can add the following code in the Tests tab of your auth request:
var jsonData = JSON.parse(responseBody);
pm.globals.set("id_token", jsonData.idToken);

Send the post request to generate token

For your Postman requests, on another tab:
set the Bearer Token in Authorization to {{id_token}}

Test token by logging with console.log(pm.globals.get("id_token"));