The following section of this book requires that we do this work in Linux as the requirements are only available on that platform. When Selenium is running on your machine, you will see that it always runs on your screen. If you want to push the running of your tests to a background, then you will need to use something like XVFB. XVFB stands for X11 Virtual Frame Buffer.
This allows us to run tests with a real browser without it trying to steal focus from you. FirefoxDriver, for example, forces the browser to the foreground to help the native events.