hi, we are currently aware about this on some windows 8 configurations with amd graphics cards and older drivers. please see if there's a more recent graphics driver available for your system at https://support.amd.com/en-us/download and if installing that already solves the playback issue. otherwise you can do the following to work around the problem: enter '''about:config''' into the firefox address bar (confirm the info message in case it shows up) & search for the preference named '''media.windows-media-foundation.use-nv12-format'''. double-click it and change its value to '''false'''.