There are really two issues here:
1) I installed libflashsupport because rhythmbox wouldn't play audio if a flash player was opened in firefox before (after a new login) and vise versa. If rhythmbox opened first, I couldn't hear, for example, audio on youtube. After searching around, I found http://mylinuxnotebook.blogspot.com/2008/07/ubuntu-sound-flash-problem.html who had the same issue. I installed libflashsupport and the problem described went away.
2) Now however, the issue is that I can't view some flash video (most notably The Daily Show). Whenever I try to open a new video, the browser (firefox or epiphany) crashes after loading all but the main video. After searching for the issue, I found http://techblog.ralph-schuster.eu/2008/07/28/firefox-3-crash-on-linux-with-flash/ and tried his solution. This did not work: neither removing the audio support nor disabling ad block plus changed anything. However, what did fix the problem was removing libflashsupport.
Thank you for reporting this bug. Please give us your ubuntu version and the outputs of "apt-cache policy libflashsupport" "apt-cache policy firefox" and "apt-cache policy epiphany".