I have 5.0.1 on mine. Still waiting for 5.1.1...
Keep in mind that by default the Facebook app auto plays all videos in your feed. You need to disable that.I'm new to Android phones so I don't know a lot about researching the bugs. My biggest gripe is the battery, especially coming from the iPhone. Yesterday, I had some slowness but I think it might be because the facebook app was still in the background, not sure. Usually it's a decent phone. I like being able to have tons of options for certain tasks.