Facebook has developed an open-sourced Network Connection Class that will allow the company to determine the speed of the data connection you have when connecting to your News Feed. Based upon the speeds that are returned, Facebook has made some optimizations to how content is delivered, in order to offer a better experience.
People are coming online at a staggering rate in emerging markets and, in most cases, are doing so on mobile via 2G connections. In order to make sure another billion people can connect using Facebook we need to design features of the product that work seamlessly regardless of mobile network and device. What this means for those of us on the News Feed team is making sure people can load and scroll through News Feed on any connection speed.
Facebook will take connection speed into account, and on slow connections the app will download only the stories you are looking at first. Normally, Facebook loads a variety of content in the background, like other stories and photos, but on lower data speeds it will now only load what you are looking at. Additionally, Facebook is exploring which image formats load best on lower speeds, and recently migrated to a progressive JPEG which allows for a lower-quality version to be shown while the image is still downloading. Finally, Facebook will now show stories that you have previously loaded when on a poor connection, instead of loading nothing at all. If something about the story has changed, Facebook will update those parts of information, but will not reload everything.