Download the installer from http://www.java.com/en/download/manual.jsp

cd /usr/local/
mkdir java
cd java
sh /home/user/location_of_jre_installer/jre-6u3-linux-i586.bin
cd /usr/local/firefox/plugin/	[The folder where firefox is installed]
ln -s /usr/local/java/jre1.6.0_03/plugin/i386/ns7/libjavaplugin_oji.so