: It uses significantly less data and system resources than the standard app.

You downloaded an incomplete APK or one built for a different CPU (e.g., x86 instead of ARM). Fix: Delete the file. Clear cache of Package Installer (Settings > Apps > All > Package Installer > Clear Data). Re-download the APK from a trusted mirror.

If APKs are still lagging, the "solid" move is to avoid the app entirely. Open your mobile browser and go to m.facebook.com

This guide is for nostalgia or emergency use. If your phone is running Android 4.1.2, you face two major risks: