In the case of Vines and Instagram videos, the audio will play but the video won't. On Twitter, scrolling over gifs/Vines turns them black and/or they do not play. My Flash Player is updated. In about:config, media.windows-media-foundation.enabled is set to true. I've tried setting to false, which just turns off the audio, and switching it back to true, which does nothing. I've reset Firefox. I've re-downloaded it. Nothing seems to be working. Solutions? Edit: Restarting in SafeMode makes it work, so it must be one of the add ons. Edit #2: Figured it out. For those who have the same problem, so to Options -->Advanced --> General and uncheck the Use Hardware Acceleration Where Available box.