Using FireTube is really simple. Just tap on a video for it to start playing automatically in the music mode. Instead of watching the video, as with other apps, you'll see a still image while you listen to the audio. This way, the app consumes much less data from your plan.
Once the audio starts playing you can close the app or turn off the screen. Don't worry, the sound keeps playing without any problems. You can even pause the music and change songs just like you'd do with any other music player.
FireTube is an excellent app that basically transforms the entire content of YouTube into your new music library. The best thing about it is that you can log in with your YouTube account and listen to your own custom playlists.