Playing media (on any website) at a faster playback speed than 1x will result in a messed up audio waveform. I played a 60 HZ Test Tone video (https://youtu.be/GqwFimG3X3w) and used audacity to record my stereo-mix device to show the audio waveform that I hear. I have attached a picture which shows the waveforms for Firefox and Chrome at 1x and 2x playback speed. The results for Internet Explorer are the same as Chrome. This is the first time that I have installed Firefox on this laptop. The extensions that I use are uBlock and h264ify. I have disabled them both and tested again, but the problem remained. The image I uploaded isn't showing, so I uploaded it to imgur. https://imgur.com/XAz5ph4