Facebook isn't just content to provide the best experience on high-end mobile phones or those with with a quick mobile network. A team of product managers and engineers traveled to Africa to take a look at how the Facebook Android app performs in developing countries. They purchased several different Android mobile phones to test the latest version of the Facebook app. Unsurprisingly, the app didn't fare that well on the lower-end models; it would either crash constantly, or load very slowly. The team also found that they went through a month's worth of data plan within 40 minutes.
After returning to their respective offices, the team began to work on improving the app. And what followed was improvements in performance, data efficiency, networking, and application size. The app now fetches stories earlier in the start process so the app has more time to set up connections and download the News Feed. As a result the start times of the app were reduced by more than 50%. The Android app now also uses Google's WebP format to transmit Facebook images, and has achieved 25 to 35 percent data savings when compared with JPG, and 80 percent compared with PNG. This helps to cut down unnecessary data consumption, and the app will now only load images in resolutions that will match your device's screen size. The Facebook app size has also been reduced by 65% in order to work with phones that have limited RAM or storage capacities.
Source: Facebook Engineering Blog