A Mobile First Development developer primarily focuses on designing and developing applications for mobile devices. They start the development process with mobile in mind, rather than it being an afterthought. Their tasks include creating responsive designs to ensure optimal viewing and interaction experience across various devices, programming and coding for mobile platforms, and optimizing applications for maximum speed and scalability. These developers also ensure that the mobile user interface is user-friendly, efficient, and appealing. They often collaborate with cross-functional teams to define feature specifications and develop high-quality solutions that meet customer needs.