Install flash plug-in

When you guys normally start working on Firefox, the default web browser in Ubuntu, the You-tube or other video players may not work and ask to install flash plug-ins. 

You can either download a .tar.gz file from
http://get.adobe.com/flashplayer/?promoid=JZEFT and extract manually

Or simply use this code in Terminal

sudo apt-get install flashplugin-installer

you will be prompted to enter the password, hit and enter.