How do I resize the window in Chrome and Firefox when testing with Selenium?

For Chromejust add before "webdriver.Chrome" init:

chrome_options.add_argument("--window-size=1920x1080")

For all browsers:

There is an official selenium python binding for that: http://selenium.googlecode.com/git/docs/api/py/webdriver_remote/selenium.webdriver.remote.webdriver.html#selenium.webdriver.remote.webdriver.WebDriver.set_window_size

driver.set_window_size(1920, 1080)

or

driver.maximize_window()

or with javascript

driver.execute_script("window.resizeTo(1920,1080)")