The article provides an in-depth exploration of how web browsers work, highlighting the transition from the dominance of Internet Explorer to the current landscape where open-source browsers like Firefox and Chrome prevail. It delves into the primary components of a browser, such as the user interface, browser engine, rendering engine, JavaScript interpreter, networking, and data storage, and describes the process flow from receiving HTTP requests to rendering content on the screen. The rendering engine processes HTML and CSS to create a DOM tree and render tree, arranging elements for display through layout and painting processes, while the z-index property influences the layered display of elements. Understanding these processes is essential for web developers to create interactive applications and test website compatibility across different browsers, emphasizing the importance of tools like LambdaTest for cross-browser testing. The article concludes by encouraging developers to deepen their understanding of browser functionality to optimize their development and testing practices.