So.... when I came back from a long december holiday, my openSUSE 11 machine had a lot of updates to install.
One of them was the flash player update which plugs the huge security hole that was found.
After this update my sound in flash movies (like youtube) was crap: choppy and halting sound. That sucks!
At first I restored the old version, which worked, but then I was vulnerable again. So to resolve this, I installed the downloaded version from the adobe website which is currently at version 10.0.0.15.3.
The easiest way to do this, is download the tar.gz file from adobe, and extract it:
$ tar xzvf install_flash_player_10_linux.tar.gz
Next, go into the install_flash_player_10_linux directory and copy the file libflashplayer.so to /usr/lib/browser-plugins. You must be root to write to that location.
Restart firefox and you're done: (near) perfect sound.