- Support for WebDriver-conforming [New Session](https://w3c.github.io/webdriver/webdriver-spec.html#dfn-new-session) negotiation, with `desiredCapabilities`/`requiredCapabilities` negotiation as fallback
- Added two new endpoints:
- GET `/session/{session id}/window/rect` for [Get Window Rect](https://w3c.github.io/webdriver/webdriver-spec.html#get-window-rect)
- POST `/session/{session id}/window/rect` for [Set Window Rect](https://w3c.github.io/webdriver/webdriver-spec.html#set-window-rect)
- Align errors with the [WebDriver errors](https://w3c.github.io/webdriver/webdriver-spec.html#handling-errors):
- Introduces new errors [`ElementClickIntercepted`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.ElementClickIntercepted), [`ElementNotInteractable`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.ElementNotInteractable), [`InvalidCoordinates`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.InvalidCoordinates), [`NoSuchCookie`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.NoSuchCookie), [`UnableToCaptureScreen`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.UnableToCaptureScreen), and [`UnknownCommand`](https://docs.rs/webdriver/0.25.0/webdriver/error/enum.ErrorStatus.html#variant.UnknownCommand)
- Removes `ElementNotVisible` and `InvalidElementCoordinates` errors
### Removed
- Removed following list of unused endpoints:
- GET `/session/{session id}/alert_text`
- POST `/session/{session id}/alert_text`
- POST `/session/{session id}/accept_alert`
- POST `/session/{session id}/dismiss_alert`
- GET `/session/{session id}/window_handle`
- DELETE `/session/{session id}/window_handle`
- POST `/session/{session id}/execute_async`
- POST `/session/{session id}/execute`
### Changed
- [`SendKeysParameters`](https://docs.rs/webdriver/0.25.0/webdriver/command/struct.SendKeysParameters.html), which is used for the [Element Send Keys](https://w3c.github.io/webdriver/webdriver-spec.html#element-send-keys) and [Send Alert Text](https://w3c.github.io/webdriver/webdriver-spec.html#send-alert-text) commands, has been updated to take a string `text` field
- [`CookieResponse`](https://docs.rs/webdriver/0.25.0/webdriver/response/struct.CookieResponse.html) and [`CloseWindowResponse`](https://docs.rs/webdriver/0.25.0/webdriver/response/struct.CloseWindowResponse.html) fixed to be properly wrapped in a `value` field, like other responses
- Allow negative numbers for `x` and `y` fields in `pointerMove` action
- Disable Flash and the plugin container in Firefox by default, which should help mitigate the “Plugin Container for Firefox has stopped wroking” problems [many users were reporting](https://github.com/mozilla/geckodriver/issues/225) when deleting a session
- Preferences passed in a profile now take precedence over set of default preferences defined by geckodriver (fixed by [@DrMarcII](https://github.com/DrMarcII))
- The exceptions are the `marionette.port` and `marionette.log.level` preferences and their fallbacks, which are set unconditionally and cannot be overriden
- Remove default preference that disables unsafe CPOW checks
- Fix for the “corrupt deflate stream” exception that sometimes occured when trying to write an empty profile by [@kirhgoph](https://github.com/kirhgoph)
- All HTTP responses are now wrapped in `{value: …}` objects per the WebDriver specification; this may likely require you to update your client library
- Pointer move action’s `element` key changed to `origin`, which lets pointer actions originate within the context of the viewport, the pointer’s current position, or from an element
- Now uses about:blank as the new tab document; this was previously disabled due to [bug 1333736](https://bugzilla.mozilla.org/show_bug.cgi?id=1333736) in Marionette
- Aligned the data structure accepted by the [Set Timeouts](https://w3c.github.io/webdriver/webdriver-spec.html#set-timeouts) command with the WebDriver specification
- When navigating to a document with an insecure- or otherwise invalid TLS certificate, an [insecure certificate](https://w3c.github.io/webdriver/webdriver-spec.html#dfn-insecure-certificate) error will be returned
- On macOS, deducing Firefox’ location on the system will look for _firefox-bin_ on the system path (`PATH` environmental variable) before looking in the applications folder
- Window position coordinates are allowed to be negative numbers, to cater for maximised window positioning on Windows
- WebDriver library updated to version 0.18.0
### Fixed
- Check for single-character key codes in action sequences now counts characters instead of bytes
- Added [_Take Element Screenshot_](https://w3c.github.io/webdriver/webdriver-spec.html#take-element-screenshot) command
- Added new [_Status_](https://w3c.github.io/webdriver/webdriver-spec.html#status) command
- Added routing for the [_Get Timeouts_](https://w3c.github.io/webdriver/webdriver-spec.html#get-timeouts) command, but it is not yet implemented in Marionette, and will return an _unsupported operation_ error until it is
- Implemented routing for [new actions API](https://w3c.github.io/webdriver/webdriver-spec.html#actions), but it too is not yet fully implemented in Marionette
- [Synced Firefox preferences](https://github.com/mozilla/geckodriver/commit/2bfdc3ec8151c427a6a75a6ba3ad203459540495) with those used in Mozilla automation
- Added new extension commands for finding an element’s anonymous children and querying its attributes; accessible through the `/session/{sessionId}/moz/xbl/{elementId}/anonymous_children` to return all anonymous children and `/session/{sessionId}/moz/xbl/{elementId}/anonymous_by_attribute` to return an anonymous element by a name and attribute query
- The `binary`, `args`, and `profile` entries on this dictionary is equivalent to the old `firefox_binary`, `firefox_args`, and `firefox_profile` capabilities, which have now all been removed
- The `log` capability takes a dictionary such as `{log: "trace"}` to enable trace level verbosity in Gecko
- The `prefs` capability lets you define Firefox preferences through capabilities
-`firefox_binary`, `firefox_args`, and `firefox_profile` capabilities removed in favour of the `moz:firefoxOptions` dictionary detailed above and in the README
- Verbosity shorthand flag `-v[v]` now works again, following the replacement of the argument parsing library in the previous release
- When the HTTPD fails to start, errors are propagated to the user
- Disabled the additional welcome URL (`startup.homepage_welcome_url.additional`) so that officially branded Firefox builds do not start with two open tabs in fresh profiles
- Disabled homepage override URL redirection on milestone upgrades, which means a tab with an upgrade notice is not displayed when launching a new Firefox version
