Intalling Java plugin

Download the Java from http://java.com/en/download/ (in this cases version 7 update 13).

As root user:

- Make a Java directory, for example

mkdir /usr/java

- Uncompress the downloaded file in it

tar zxvf jre-7u7-linux-i586.tar.gz -C /usr/java

- Create the symbolic link from your browser to the java plugin

cd /usr/lib/mozilla/plugins/
ln -s /usr/java/jre1.7.0_13/lib/$YOUR_ARCH/libnpjp2.so .

(replace  YOUR_ARCH with amd64 or i386, etc)

Restart your browser.

Test your installation http://java.com/en/download/testjava.jsp


Source:  http://java.com/en/download/help/linux_install.xml