I am having the same problem. I have downgraded selenium for now.

pip uninstall selenium

pip install selenium==3.3.1

Question: org.openqa.selenium.webdriverexception: unknown error: call function result missing 'value'. Please look into below steps to resolve such error.

Answer: Update browser version. Please follow below steps to get the latest version of browsers.

1. Go to: https://www.seleniumhq.org/download/
2. CTRL+F and search "Third Party Browser Drivers". All browsers are listed there.
3. Click on browser name/version -It redirects to the another page. (E.g.- http://chromedriver.storage.googleapis.com/index.html?path=2.36/)
4. Download appropriate driver for your operating system.
5. Place driver into one of folder from where you are calling that driver to your selenium webdriver scripts. It works without any error.

Thanks :) !!