During the past month, both Google and Mozilla developers have added support in their respective browsers for "headless mode," a mechanism that allows browsers to run silently in the OS background and with no visible GUI.
Until now, headless browsers were forks of well-known browser engines adapted to run in headless mode, used only by developers for automated tests.
This type of testing is crucial in modern web development, as it allows developers to see how a page responds to certain actions such as page loads, clicks on buttons, filling in forms, etc..
Usually, developers log all these responses, such as page load times and action response times, and later analyze the results to make improvements to their sites.
Full Article.