GitHub has introduced a new feature for its Mac and Windows applications that allows users to open files directly from pull requests and branches. By clicking the new "Open" button, users can launch GitHub for Mac or Windows to clone the repository if it's not already on their device, switch to the branch with the changes, and open the file in its default application for editing. This enhancement aims to streamline the process of addressing comments on pull requests, making it more efficient for developers to manage changes and collaborate on code.