Release v0.21.0 · mozilla/geckodriver

Note that with this release of geckodriver the minimum recommended
Firefox and Selenium versions have changed:

Support for the chrome element identifier from Firefox.
The unhandledPromptBehavior capability now accepts accept and notify, dismiss and notify, and ignore options.

Note that the unhandled prompt handler is not fully supported in
Firefox at the time of writing.

Firefox will now be started with the -foreground and -no-remote
flags if they have not already been specified by the user in
moz:firefoxOptions.

-foreground will ensure the application window gets focus when
Firefox is started, and -no-remote will prevent remote commands
to this instance of Firefox and also ensure we always start a new
instance.
WebDriver commands that do not have a return value now correctly
return {value: null} instead of an empty dictionary.
The HTTP server now accepts Keep-Alive connections.
Firefox remote protocol command mappings updated.

All Marionette commands changed to make use of the WebDriver:
prefixes introduced with Firefox 56.
Overhaul of Firefox preferences.

Already deprecated preferences in Firefox versions earlier than
57 got removed.
webdriver crate upgraded to 0.36.0.

Force use of IPv4 network stack.

On certain system configurations, where localhost resolves to
an IPv6 address, geckodriver would attempt to connect to Firefox
on the wrong IP stack, causing the connection attempt to time out
after 60 seconds. We now ensure that geckodriver uses IPv4
consistently to both connect to Firefox and for allocating a free
port.
geckodriver failed to locate the correct Firefox binary if it was
found under a firefox or firefox-bin directory, depending on
the system, because it thought the parent directory was the
executable.
On Unix systems (macOS, Linux), geckodriver falsely reported
non-executable files as valid binaries.
When stdout and stderr is redirected by geckodriver, a bug prevented
the redirections from taking effect.

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