In Selenium why does Firefox requires GeckoDriver

Question

I wanted to use Selenium with all the 3 Browsers, So, I wrote the following different codes:

FirefoxDriver driver = new FirefoxDriver();
ChromeDriver driver = new ChromeDriver();
InternetExplorerDriver driver = new InternetExplorerDriver();

With Chrome and IE  it works fine, but it throws the following error with firefox:

"The geckodriver.exe file does not exist in the current directory or in a directory on the PATH environment variable"

Why does firefox requires geckoDriver?

Answer 1

Firefox requires GeckoDriver because:

For Mozilla Firefox till version 47, we didn't need geckoDriver. But the Mozilla Firefox after version 47, comes with Marionette, which is an automation driver for Mozilla's  It can remotely control either the UI or the internal JavaScript of a Gecko platform, such as Firefox. So, we require GeckoDriver for FireFox.