download_firefox.py

import time
from browsermobproxy import Server
server = Server('/Users/dhunt/Downloads/browsermob-proxy-2.0-beta-6/bin/browsermob-proxy')
server.start()
proxy = server.create_proxy()

from selenium import webdriver
profile = webdriver.FirefoxProfile()
profile.set_proxy(proxy.selenium_proxy())
driver = webdriver.Firefox(firefox_profile=profile)

proxy.new_har('firefox')
driver.get('http://www.mozilla.org/')
download_buttons = driver.find_elements_by_class_name('download-firefox')

for button in download_buttons:
    if button.is_displayed():
        break
    else:
        continue

button.click()
time.sleep(10)
assert proxy.har['log']['entries'][-1]['request']['url'] == 'http://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/15.0/mac/en-US/Firefox%2015.0.dmg'
time.sleep(10)
assert proxy.har['log']['entries'][-1]['response']['status'] == 200
assert proxy.har['log']['entries'][-1]['response']['content']['mimeType'] == 'application/x-apple-diskimage'
assert proxy.har['log']['entries'][-1]['response']['content']['size'] == 34139395