After install my Ubuntu 12.04 and setup it I try to access my online banking. I couldn't access it, because the Java wasn't there. So here is how to Install Java on Ubuntu 12.04 (64 bits) and use it on firefox.
$ sudo apt-get install icedtea6-plugin
Now to have your Java working on firefox use:
$ sudo apt-get install icedtea-plugin
Close your browser, open and enjoy.