Selenium and Capybara are used for cross-browser testing and remote file uploads can be achieved through the use of a FileDetector object. The FileDetector is an object that determines if a given string represents a file, and its presence allows Selenium to upload files remotely. To enable remote file uploads in Capybara, a FileDetector object needs to be set on the Selenium driver, which will then check for the existence of the file path provided before uploading it. This process eliminates the need for manual checks within the FileDetector lambda, making the implementation straightforward and efficient.