A frontend testing developer is responsible for validating the functionality, usability, and accessibility of a website or application's user interface. They design, implement, and execute automated and manual test cases to ensure the frontend code works as expected across various browsers and devices. Their job requires identifying bugs, reporting them, and working closely with frontend developers to rectify the issues. They use tools like Selenium, Jest, or Mocha for automated testing. They also ensure the design aligns with the UX/UI specifications and the application is user-friendly, responsive, and visually appealing.