$ sudo apt-get update
$ sudo apt-get install icedtea6-plugin 

icedtea6-plugin is installed in your system.

Make ensure the icedtea6-plugin package were installed using the commands given below,

$ sudo dpkg-query -l | grep icedtea6-plugin *

You will get with icedtea6-plugin package name, version, architecture and description in a table

icedtea6-plugin package basic information: