Video stream (Twitch.tv) on a background tab loses quality

After one of recent Firefox updates twitch.tv streams do not work properly for me. When stream is going on a non-active tab it starts slowly lose quality over time, although in a twitch player video is set to max quality. When i switch back to stream tab, i see pixelated video for a few seconds and then it restores to proper quality. Sometimes stream stops completely if i have not visited that tab for awhile. How do i fix this?