AntiDuck

After Firefox update to 48.0.2, H264 video stopped playing in Windows XP SP3 Well, it took me two nights to find this post, Thank you very-very-very much! In my case, Adobe DRM was installed, but somehow Decoder option was disabled. So I just put media.gmp.decoder.enabled = true, and this helped. You won't believe how much crazy stuff people write about this problem - including registry tweaks, system files manual copying, dll re-registering ... I'm happy you were here to help with just Firefox config settings! Great thanks!