Flash Problem in Firefox

[Roger]

  I am trying to run up new install of Fedora 11.
  I go into Firefox 3.5.3-1.fc11 and attempt to run a YouTube vid.
I get a message stating
I had the same for a while.
there is a switch in preferences that tells firefox that the apps are 
available.
and You've got to run the firefox plugins diaolog.
I don't know the details as my daughter did it for me but since then its 
worked very well for me.
Roger