Icecat audio/video problems

I seem to be experiencing some problems with audio/video in Icecat (security-focused derivative of Firefox) , for example when trying to play You Tube videos. Frequently, I start playing a video and either the audio is strange and garbled, or the video doesn't seem to play properly at all - when I press 'play', it plays for half a second and then stops. I am using Icecat in Parabola (derivative of Arch), with pulseaudio in LXDE. I installed the Parabola system recently and carried over my user home directory from a previous GNU/Linux installation. I tried creating a new user from scratch and if I log in to LXDE as the new user, the audio/video in icecat seems to work much better - You Tube videos seem to play flawlessly. So, I suspect the issue with the legacy user account is to do with some of the user settings files in the home directory being carried over from the previous system. Does anyone have any idea what files might be affecting this?