In preparation for the upcoming implementation of WebDriver BiDi  we
are going to reorganize the build flags for Marionette
(--disable-marionette) and the Remote Protocol (--enable-cdp)  into a
single WebDriver (--disable-webdriver) one. This will soon be required
because the protocol implementations will start sharing code.
By default both components are enabled by default, and as long as none
of the build flags have been added to your mozconfig this change will be
transparent for you.
Otherwise please start using `--disable-webdriver` to stop building any
WebDriver specific code once Bug 1695031  has been landed on
Senior Software Engineer