To get firefox to play flash movies in ubuntu do the following. First make sure you have the adobe flash player installed:

aptitude install flashplugin-installer

This should enable flash in firefox after restarting firefox. One additional problem i had is due to compiz the flash movie player would show up in firefox. But pressing the play button had no effect. Do the following:

Edit the file: /usr/lib/nspluginwrapper/i386/linux/npviewer and add the following line:

export GDK_NATIVE_WINDOWS=1

Thats it have fun watching flash movies on ubuntu