selenium报错

Python 2.7.15

selenium 2.53.6

Firefox    47.0.1

pycharm 2017.3.7

# coding:utf-8 
from selenium import webdriver
import time 
driver =webdriver.Firefox() 
driver.get("https://www.baidu.com") 
time.sleep(3) 
driver.set_window_size(400, 600)

D:\hyz\install\python\test\venv\Scripts\python.exe D:/hyz/install/python/test/test_project/test01.py

Traceback (most recent call last):  

File "D:/hyz/install/python/test/test_project/test01.py", line 7, in <module>    

driver.set_window_size(400, 600)  

File "D:\hyz\install\python\test\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 1090, in set_window_size

    self.set_window_rect(width=int(width), height=int(height))  

File "D:\hyz\install\python\test\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 1182, in set_window_rect    

"height": height})['value']  

File "D:\hyz\install\python\test\venv\lib\site-packages\selenium\webdriver\remote\webdriver.py", line 321, in execute    

self.error_handler.check_response(response)  

File "D:\hyz\install\python\test\venv\lib\site-packages\selenium\webdriver\remote\errorhandler.py", line 242, in check_response    

raise exception_class(message, screen, stacktrace)

selenium.common.exceptions.WebDriverException: Message: POST /session/458a0cb1-1d25-445f-9f2f-17b7536a770e/window/rect did not match a known command

Process finished with exit code 1