Start by creating a Google Cloud project if you haven't already. Go to the Google Cloud Console, click on "Select a Project," and then "New Project." Name your project and click "Create." Ensure that you have the Firestore and Cloud Storage APIs enabled for your project.

Download and install the Google Cloud SDK on your local machine. This SDK allows you to interact with your Google Cloud project from your terminal. After installation, open your terminal and authenticate your account by running `gcloud init` and follow the prompts to log in and set your default project.

Ensure your CSV file is formatted correctly, with the first row containing headers corresponding to your Firestore document fields. Clean the data as necessary to ensure consistency, such as date formats or number precision.

Write a Python script that reads your CSV file and prepares the data for insertion into Firestore. Use Python's built-in `csv` library to open and parse the CSV file. Example code snippet:
```python
import csv

def read_csv(file_path):
with open(file_path, mode='r') as file:
csv_reader = csv.DictReader(file)
data = [row for row in csv_reader]
return data
```

Use the `google-cloud-firestore` Python library to interact with Firestore. Install the library using `pip install google-cloud-firestore`. Then, set up the Firestore client in your script using your Google Cloud credentials. Ensure your service account key is downloaded and set up:
```python
from google.cloud import firestore

# Initialize Firestore
db = firestore.Client()
```

Create a function in your script to upload the parsed CSV data to Firestore. Iterate over each row and insert it as a document into a specified Firestore collection:
```python
def upload_to_firestore(data, collection_name):
for row in data:
# Add each row as a new document
db.collection(collection_name).add(row)

# Example usage
csv_data = read_csv('your-file.csv')
upload_to_firestore(csv_data, 'your-collection-name')
```

Execute your Python script to start the data transfer process. Check the Firestore console at https://console.firebase.google.com/ to verify that your data has been correctly uploaded to the specified collection. Ensure that the data integrity is maintained and troubleshoot any errors as needed.

By following these steps, you can efficiently move data from a CSV file into Google Firestore without relying on any third-party connectors or integrations.