Added

• New --jsdebugger flag to open the Browser Toolbox when Firefox
  launches. This is useful for debugging Marionette internals.

• Introduced the temporary, boolean capability
  moz:useNonSpecCompliantPointerOrigin to disable the WebDriver
  conforming behavior of calculating the Pointer Origin.

Changed

• HTTP status code for the StaleElementReference error changed
  from 400 (Bad Request) to 404 (Not Found).

• Backtraces from geckodriver no longer substitute for missing
  Marionette stacktraces.

• webdriver crate upgraded to 0.35.0.

Fixed

• The Firefox process is now given ample time to shut down, allowing
  enough time for the Firefox shutdown hang monitor to kick in.

  Firefox has an integrated background monitor that observes
  long-running threads during shutdown. These threads will be
  killed after 63 seconds in the event of a hang. To allow Firefox
  to shut down these threads on its own, geckodriver has to wait
  that time and some additional seconds.

• Grapheme clusters are now accepted as input for keyboard input
  to actions.

  Input to the value field of the keyDown and keyUp action
  primitives used to only accept single characters, which means
  geckodriver would error when a valid grapheme cluster was sent in,
  for example with the tamil nadu character U+0BA8 U+0BBF.

  Thanks to Greg Fraley for fixing this bug.

• Improved error messages for malformed capability values.