Another option is to use a browser specifically designed with data-saving in mind, such as Opera Mini.
2. Turn off Facebook's auto-play videos
All those videos of babies and puppies and babies riding puppies that auto-play in your Facebook feed? They eat up a lot of data. In Android, turn off auto-play by opening Facebook, going to Settings, and switching "Videos auto-play" to Off or Wi-Fi Only. In iOS, go to Settings, select Facebook, Settings, then switch Auto-play to On or Off under Video.