Automating GMAIL login using Python-Selenium

I am trying to automate logging into GMail using Selenium package of Python. However, I am not able to accomplish the task and get the following error:

Traceback (most recent call last):
  File "C:\Users\Surojit\Desktop\Python\automaticpasswordFiller.py", line   21, in <module>
    passwordElem = browser.find_element_by_id('Passwd')
  File "C:\Users\Surojit\AppData\Local\Programs\Python\Python35-32\lib\site- packages\selenium\webdriver\remote\webdriver.py", line 266, in  find_element_by_id
    return self.find_element(by=By.ID, value=id_)
  File "C:\Users\Surojit\AppData\Local\Programs\Python\Python35-32\lib\site- packages\selenium\webdriver\remote\webdriver.py", line 744, in find_element
    {'using': by, 'value': value})['value']
  File "C:\Users\Surojit\AppData\Local\Programs\Python\Python35-32\lib\site-  packages\selenium\webdriver\remote\webdriver.py", line 233, in execute
    self.error_handler.check_response(response)
  File "C:\Users\Surojit\AppData\Local\Programs\Python\Python35-32\lib\site- packages\selenium\webdriver\remote\errorhandler.py", line 194, in check_response
    raise exception_class(message, screen, stacktrace)
selenium.common.exceptions.NoSuchElementException: Message: Unable to locate  element: {"method":"id","selector":"Passwd"}
Stacktrace:
    at FirefoxDriver.prototype.findElementInternal_   (file:///C:/Users/Surojit/AppData/Local/Temp/tmpceecsm46/extensions/fxdriver@goo glecode.com/components/driver-component.js:10770)
     at FirefoxDriver.prototype.findElement   (file:///C:/Users/Surojit/AppData/Local/Temp/tmpceecsm46/extensions/fxdriver@goo  glecode.com/components/driver-component.js:10779)
    at DelayedCommand.prototype.executeInternal_/h   (file:///C:/Users/Surojit/AppData/Local/Temp/tmpceecsm46/extensions/fxdriver@goo    glecode.com/components/command-processor.js:12661)
    at DelayedCommand.prototype.executeInternal_    (file:///C:/Users/Surojit/AppData/Local/Temp/tmpceecsm46/extensions/fxdriver@goo glecode.com/components/command-processor.js:12666)
    at DelayedCommand.prototype.execute/<   (file:///C:/Users/Surojit/AppData/Local/Temp/tmpceecsm46/extensions/fxdriver@googlecode.com/components/command-processor.js:12608) 

The simple code that I have written is:

from selenium import webdriver
from selenium.webdriver.common.keys import Keys
from selenium.webdriver.common.by import By
import time

browser = webdriver.Firefox()
browser.get('http://gmail.com')
action = webdriver.ActionChains(browser)
emailElem = browser.find_element_by_id('Email')
emailElem.send_keys("MyUserName")
browser.find_element_by_name('signIn').click()
#browser.get('https://accounts.google.com/ServiceLogin?         service=mail&continue=https://mail.google.com/mail/#password')
passwordElem = browser.find_element_by_id('Passwd')
passwordElem.send_keys("MyPassword")
browser.find_element_by_name('signIn').click()

Also, I have tried to find out the error in my code by comparing it to an answer given to a similar question here at: Auto connect on my Gmail account with Python Selenium

Can someone please guide me on the right path and let me know where I am making a mistake?

P.S: This is my first post on stackoverflow. Please excuse me for any mistake that I have made in posting the question