profile = webdriver.FirefoxProfile()
profile.set_preference('browser.download.folderList', 2)
profile.set_preference('browser.download.manager.showWhenStarting', False)
profile.set_preference('browser.download.dir', 'PATH TO DESKTOP')
profile.set_preference('browser.helperApps.neverAsk.saveToDisk',
    'application/x-gzip')
driver = webdriver.Firefox(firefox_profile=profile)
driver.get("Name of web site I'm grabbing from")
driver.find_element_by_xpath("//a[contains(text(), 'DEV.tgz')]").click()
Downloading file to specified location with Selenium and python