Begin by clearly defining what data you need to move from Drift to Firestore. Identify the specific data fields in Drift that are necessary and how you want them organized in Firestore. This preparation ensures a focused approach and avoids unnecessary data transfer.

Drift provides an API that allows you to programmatically access data. Obtain your Drift API credentials by logging into your Drift account and navigating to the API settings. Note down the API key, as you will need it to authenticate and access the data you require.

Write a script in a programming language like Python or Node.js to extract the necessary data from Drift using their API. Use HTTP requests (e.g., `GET` method) to fetch data from Drift endpoints. For example, to get user information, you would target the relevant endpoint and parse the JSON response to extract data.

Ensure your Google Firestore is set up within your Firebase project. If not already done, create a Firebase project at the Firebase console. Inside your project, access Firestore and create the necessary collections and documents structure that will mirror the data you extracted from Drift.

Go to the Firebase console, navigate to Project Settings, and generate a new private key for a service account. Download the JSON key file. This file will be used to authenticate your script to access Firestore securely.

Modify your script to process the data extracted from Drift and format it to match the Firestore document structure. Use the Firebase Admin SDK in your script to authenticate with the Firestore service account credentials and upload the data. You will typically perform operations like `add` or `set` to insert or update documents in Firestore.

After the data transfer, manually review a subset of the data in Firestore to ensure it has been correctly and completely transferred. Check for consistency, accuracy, and any potential discrepancies. Perform spot checks and run queries to validate the data against the original data from Drift.

By following these steps carefully, you can successfully move your data from Drift to Google Firestore without relying on third-party connectors or integrations, maintaining control over the data handling process.