1. Open the Command Prompt (Terminal).
2. Enter the command given below to install Flash player:
sudo apt-get install flashplugin-nonfree
Your flash player is supposed be working. Go to Youtube to see flash content.
Troubleshooting:Note: This issue is applicable to older Ubuntu Linux versions such as 6.04.
Someone may observe issues related with audio/voice in newly installed flash player.
Enter following commands to resolve this trouble:
sudo apt-get install alsa-oss
gksudo gedit /etc/firefox/firefoxrc
Find a line that reads FIREFOX_DSP and make it:
Save the file and Exit.
Restart the Firefox.