You will find that if you are running the 64-bit version of Ubuntu and installed flashplugin-installer or flashplugin-nonfree, that flash controls in Firefox do not work when Compiz is enabled. To fix this, install Adobe’s 64-bit flash plugin.  Credit goes to http://ubuntuforums.org/showthread.php?t=1319541 (March 14th, 2010) for the solution that worked for me:

sudo apt-get remove flashplugin-installer flashplugin-nonfree mozilla-plugin-gnash
cd /tmp
wget 
tar xf libflashplayer-10.0.32.18.linux-x86_64.so.tar.gz
sudo mv libflashplayer.so /usr/lib/mozilla/plugins/