title: unable to set preferences for Firefox profile with Selenium (geckodriver 0.16)
body: <p>Just installed geckodriver 0.16.1 and updated firefox to 53 (64bit) and my script appears like it is not setting preferences. Here is the code I use set Firefox profile so it automatically downloads a ms word file without the download prompt.</p>
  
  <pre><code>from selenium import webdriver
  import os
  
  fp = webdriver.FirefoxProfile()
  fp.set_preference("browser.download.folderList", 2)
  fp.set_preference("browser.download.dir", os.getcwd())
  fp.set_preference("browser.download.manager.showWhenStarting", False)
  fp.set_preference("browser.helperApps.neverAsk.openFile", "application/msword")
  fp.set_preference("browser.helperApps.neverAsk.saveToDisk", "application/msword")
  driver = webdriver.Firefox(firefox_profile=fp)
  </code></pre>
  
  <p>This script worked before updating Firefox and geckodriver. Now when I run it, the download prompt appears. </p>
  
  <p>Anyone having similar issues or know what changed with geckodriver?</p>