geckodriver executable needs to be in path

from selenium import webdriver
driver = webdriver.Firefox(executable_path=r'your\path\geckodriver.exe')
driver.get('http://inventwithpython.com')

from selenium import webdriver

browser = webdriver.Firefox(executable_path='C:\ProgramData\Anaconda3\geckodriver.exe')

url = "https://github.com"

browser.close()