As "root" or using sudo (place the command 'sudo' before all commands below if not already root...
What flash plugin packages are already installed?
apt-cache pkgnames|grep -i flash
You might see "flashplugin-installer" in the list. flashplugin-installer installs the 32-bit version of Flash and a related compatibility library which may be slower and less stable, so it’s recommended to install the adobe-flashplugin package from canonial partners repository.
To enable the partners repositor open the sources.list file
vi /etc/apt/sources.list
Add the partner repositories by removing the # in front of the following lines
deb http://archive.canonical.com/ubuntu precise partner
In this example we are using Ubuntu Precise (Precise Pangolin). If you're using another version simply replace "precise" with the correct string. Now Synchronize the package index files.
apt-get update
Now update to the latest version of flash
apt-get install adobe-flashplugin
Adobe Flash Player 11.2 was released in 2012 which Adobe announced would be the last native version for Linux. This isn't a problem for Google Chrome users as the plugin is built into the browser. Firefox users are left out. However, Adobe does seem to release occasional "security" updates for 11.2 such as a recent update in late 2014