A Browser Testing developer ensures that a website or web application functions correctly across different web browsers. They perform tests on various browsers like Chrome, Firefox, Safari, and Internet Explorer to check compatibility and responsiveness. Their work involves identifying and fixing issues related to design, functionality, and performance, which may vary from one browser to another. They also need to test across different operating systems and devices, including desktops, tablets, and mobile phones. Ensuring a consistent user experience regardless of the browser used is the primary objective of a Browser Testing developer.