The release fixes a bug where geckodriver fails to find the Firefox
version number, affecting certain Linux distributions. This caused
it to fail starting new sessions. This is a consequence of the fact
that we from 0.16.0 started matching on the version number as part
of the WebDriver-conforming new session negotiation.
We have also fixed the Close Window command to properly end the
WebDriver session when the last window is closed. This will cause
Firefox to quit.
WebDriver implementation status can be tracked on MDN, and covers
both geckodriver and the Marionette remote control protocol: