...Because geckodriver implements the W3C WebDriver standard and not the same Selenium wire protocol older drivers are using, you may experience incompatibilities and migration problems when making the switch from FirefoxDriver to geckodriver. Generally speaking, Selenium 3 enabled geckodriver as the default WebDriver implementation for Firefox. With the release of Firefox 47, FirefoxDriver had to be discontinued for its lack of support for the new multi-processing architecture in Gecko. Since geckodriver is a separate HTTP server that is a complete remote end implementation of WebDriver, it is possible to avoid using the Selenium remote server if you have no requirements to distribute processes across a matrix of systems.