The error message:
Hello, you either have JavaScript turned off or an old version of
Adobe's Flash Player. Get the latest Flash player.

The above produced by
http://www.youtube.com/watch?v=z70zNOSZ160&eurl=
but also many other sites.

However, on some sites I can watch a flash movie without any problems.

Using Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.14)
Gecko/20080419 Ubuntu/8.04 (hardy) Firefox/2.0.0.14

Java and Javascript are both checked in the Firefox preferences.

Installed programs:
flashplugin-nonfree 9.0.124.0ubuntu2
java-common 0.28ubuntu3
sun-java6-bin 6-06-0ubuntu1
sun-java6-fonts 6-06-0ubuntu1
sun-java6-jre 6-06-0ubuntu1 6-06-0ubuntu1
sun-java6-bin 6-06-0ubuntu1
ubuntu-restricted-extras (multiverse is enabled)

What more can I do?

Larry