【Python】Seleniumを使ってマルチスレッドでFirefoxを起動する方法

multithread.py

from selenium import webdriver
import threading

def browser1():
    url = "https://www.google.co.jp",
    browser = webdriver.Firefox()
    browser.get(url)
    browser.close()

def browser2():
    url = "http://www.yahoo.co.jp",
    browser = webdriver.Firefox()
    browser.get(url)
    browser.close()

if __name__ == "__main__":
    th1 = threading.Thread(target=browser1)
    th2 = threading.Thread(target=browser2)

    th1.start()
    th2.start()