Copy your Google Sheets spreadsheet to Firebase using this AppScript.

google-sheets-to-firebase.gs

// Installation & Setup
//   1. Create a spreadsheet.
//   2. Under Tools > Script Editor, paste this script
//   3. Under Resources > Libraries, add two library dependencies:
//      - OAuth2: 1B7FSrk5Zi6L1rSxxTDgDEUsPzlukDsi4KGuTMorsTQHhGBzBkMun4iDF
//      - FirebaseApp: 1hguuh4Zx72XVC1Zldm_vTtcUUKUA6iBUOoGnJUWLfqDWx5WlOJHqYkrt
//   4. Create a Firebase project and initialize the Realtime Database
//   5. Fill in your project details in FIREBASE_IO_URL and SERVICE_ACCOUNT below. 
//   6. Under Resources > Cloud Platform Project, add your Firebase project's project number from GCP. You
//      can find your project number in the GCP Cloud Console here: https://console.cloud.google.com/home/dashboard?project=_
//   7. Give it a whirl from your Google Sheet! Note: you may need to click past security warnings.

// TODO: Add your Firebase project ID here. It will look something like "my-project-123"
VAR FIREBASE_IO_URL = 'https://YOUR-PROJECT-ID.firebaseio.com'

// TODO: Add your Firebase service account here. 
// Generate one by clicking "Generate new private Key" here: https://console.firebase.google.com/u/0/project/_/settings/serviceaccounts
var SERVICE_ACCOUNT = {
  "type": "service_account",
  "project_id": "XXX-XXX-XXXX",
  "private_key_id": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "private_key": "-----BEGIN PRIVATE KEY-----\XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX\n-----END PRIVATE KEY-----\n",
  "client_email": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX",
  "client_id": "01234567890123456789",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://oauth2.googleapis.com/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
};

function onOpen() {
  var ui = SpreadsheetApp.getUi();
  ui.createMenu('Publish Website')
      .addItem('Publish this sheet', 'publishSheet')
      .addItem('Publish all sheets', 'publishAllSheets')
      .addToUi();
}

function publishSheet() {
  var sheet = SpreadsheetApp.getActiveSheet();
  copySheetDataToFirebase(sheet);
}

function publishAllSheets() {
  var sheets = SpreadsheetApp.getActiveSpreadsheet().getSheets();
  for (var idx = 0; idx < sheets.length; idx++) {
    copySheetDataToFirebase(sheets[idx]);
  }
}

function copySheetDataToFirebase(sheet) {
  var logMessage = 'Publishing "' + sheet.getName() + '".';
  SpreadsheetApp.getActiveSpreadsheet().toast(logMessage, "My Website");
  
  var normalizedSheetName = normalizeHeader(sheet.getName());
  var headersRange = sheet.getRange(1,1,1,sheet.getMaxColumns());
  
  var [rows, columns] = [sheet.getLastRow(), sheet.getLastColumn()]
  var range = sheet.getRange(2,1,rows,columns);
  var data = getRowsData(sheet, range, 1);
  
  var service = getFirebaseService();
  if (service.hasAccess()) {
    var fb = FirebaseApp.getDatabaseByUrl(FIREBASE_IO_URL, service.getAccessToken())
    fb.setData(normalizedSheetName + '/', data);
  } else {
    Logger.log(service.getLastError());
  }
}
               
function reset() {
  var service = getFirebaseService();
  service.reset();
}

function getFirebaseService() {
  return OAuth2.createService('Firebase')
    .setTokenUrl('https://accounts.google.com/o/oauth2/token')
    .setPrivateKey(SERVICE_ACCOUNT.private_key)
    .setIssuer(SERVICE_ACCOUNT.client_email)
    .setPropertyStore(PropertiesService.getScriptProperties())
    .setScope('https://www.googleapis.com/auth/userinfo.email https://www.googleapis.com/auth/firebase.database');  
}


// Copied from https://gist.github.com/mhawksey/1442370

// getRowsData iterates row by row in the input range and returns an array of objects.
// Each object contains all the data for a given row, indexed by its normalized column name.
// Arguments:
//   - sheet: the sheet object that contains the data to be processed
//   - range: the exact range of cells where the data is stored
//   - columnHeadersRowIndex: specifies the row number where the column names are stored.
//       This argument is optional and it defaults to the row immediately above range;
// Returns an Array of objects.
function getRowsData(sheet, range, columnHeadersRowIndex) {
  columnHeadersRowIndex = columnHeadersRowIndex || range.getRowIndex() - 1;
  var numColumns = range.getEndColumn() - range.getColumn() + 1;
  var headersRange = sheet.getRange(columnHeadersRowIndex, range.getColumn(), 1, numColumns);
  var headers = headersRange.getValues()[0];
  return getObjects(range.getValues(), normalizeHeaders(headers));
}

// For every row of data in data, generates an object that contains the data. Names of
// object fields are defined in keys.
// Arguments:
//   - data: JavaScript 2d array
//   - keys: Array of Strings that define the property names for the objects to create
function getObjects(data, keys) {
  var objects = [];
  for (var i = 0; i < data.length; ++i) {
    var object = {};
    var hasData = false;
    for (var j = 0; j < data[i].length; ++j) {
      var key = keys[j];
      var cellData = data[i][j];
      if (isCellEmpty(cellData)) {
        continue;
      }
      
      // Clean up column-specific things
      if (key in dataCleaners) {
        cellData = dataCleaners[key](cellData);
      }
      
      // Format dates
      if (cellData.toISOString) {
        cellData = cellData.toISOString();
      }
      object[key] = escapeHtml(cellData);
      hasData = true;
    }
    if (hasData) {
      objects.push(object);
    }
  }
  return objects;
}

// Returns an Array of normalized Strings.
// Arguments:
//   - headers: Array of Strings to normalize
function normalizeHeaders(headers) {
  var keys = [];
  for (var i = 0; i < headers.length; ++i) {
    var key = normalizeHeader(headers[i], true); // alphanumeric
    if (key.length > 0) {
      keys.push(key);
    }
  }
  return keys;
}

// Normalizes a string, by removing all alphanumeric characters and using mixed case
// to separate words. The output will always start with a lower case letter.
// This function is designed to produce JavaScript object property names.
// Arguments:
//   - header: string to normalize
// Examples:
//   "First Name" -> "firstName"
//   "Market Cap (millions) -> "marketCapMillions
//   "1 number at the beginning is ignored" -> "numberAtTheBeginningIsIgnored"
function normalizeHeader(header, alphanumeric) {
  var key = "";
  var upperCase = false;
  for (var i = 0; i < header.length; ++i) {
    var letter = header[i];
    if (letter == " " && key.length > 0) {
      upperCase = true;
      continue;
    }
    if (key.length == 0 && isDigit(letter)) {
      continue; // first character must be a letter
    }
    if (upperCase) {
      upperCase = false;
      key += letter.toUpperCase();
    } else {
      key += letter.toLowerCase();
    }
  }
  
  if (alphanumeric) {
    key = key.replace(/\W/g,"");
  }
  
  return key;
}

var dataCleaners = {
  "email": function(email) {
    return email.toLowerCase();
  },
  "phoneNumber": function(phoneNumber) {
    // Strip everything except numbers and the + sign.
    return phoneNumber.toString().replace(/[^+\d]*/g, "");
  },
}

// Returns true if the cell where cellData was read from is empty.
// Arguments:
//   - cellData: string
function isCellEmpty(cellData) {
  return typeof(cellData) == "string" && cellData == "";
}

// Returns true if the character char is alphabetical, false otherwise.
function isAlnum(char) {
  return char >= 'A' && char <= 'Z' ||
    char >= 'a' && char <= 'z' ||
    isDigit(char);
}

// Returns true if the character char is a digit, false otherwise.
function isDigit(char) {
  return char >= '0' && char <= '9';
}

// Escape any double-quotes in the string.
function escapeHtml (string) {
  return String(string).replace(new RegExp('"', 'g'), '\"');
}