Ubuntu 11.04, Firefox 6.0, Shockwave Flash 10.3 r183. Every time I play a Youtube video, it starts playing the audio many times, so that I get many overlapping copies of the same audio at the same time. They play whether or not the video is paused. This doesn't happen on Vimeo, nor does it happen in Google Chrome. Any ideas?
Edit: it also happens in Youtube's HTML5 mode.