How to read the options passed by Selenium to Firefox using WebExtensions

问题

I'm starting Firefox 66 from Ruby via Selenium, this way:

profile = Selenium::WebDriver::Firefox::Profile.new
profile['foo.test'] = 123
Selenium::WebDriver::Firefox::Options.new(profile: profile)
Selenium::WebDriver.for(:firefox)

How can I get access to the foo.test in my add-on, through WebExtension API?

来源：https://stackoverflow.com/questions/57206940/how-to-read-the-options-passed-by-selenium-to-firefox-using-webextensions