After upgrading Ubuntu I had some problems with Flash not working. I read the following threads and combined information from both to solve my problem:
http://ubuntuforums.org/showthread.php?t=1244048
http://ubuntuforums.org/showthread.php?t=1373582
Run the following commands in a terminal to remove existing Flash files:
sudo apt-get remove -y –purge flashplugin-nonfree gnash gnash-common mozilla-plugin-gnash swfdec-mozilla libflashsupport nspluginwrapper
sudo rm -f /usr/lib/mozilla/plugins/*flash*
sudo rm -f ~/.mozilla/plugins/*flash*
sudo rm -f /usr/lib/firefox/plugins/*flash*
sudo rm -f /usr/lib/firefox-addons/plugins/*flash*
sudo rm -rfd /usr/lib/nspluginwrapper
sudo rm -rf /usr/lib/flashplugin*
Then run the following command to install the correct version of Flash:
sudo apt-get install flashplugin-installer
Seán Hayes 