The document discusses protocol handlers in Gecko. It explains that protocol handlers allow Gecko to interact with different URI schemes like http, ftp, file etc. It provides an overview of how the awesome bar, browser UI, DocShell and Necko components work together to handle protocol requests from inputting a URL in the awesome bar to creating a channel and loading content. It also briefly introduces channels and stream listeners in Necko which are used for asynchronous loading of content.