Download and Install Java on Ubuntu 12.04, 15.10

Download Java software for Linux
https://www.java.com/en/download/linux_manual.jsp

Install - Java for Linux Platforms
https://www.java.com/en/download/help/linux_install.xml#Java%20for%20Linux%20Platforms

sudo mkdir -p /usr/java
sudo tar xf ~/Downloads/jre-XXXXX-linux-i586.tar.gz  -C /usr/java/

Enable and Configure
https://www.java.com/en/download/help/linux_install.xml#enable

killall firefox-bin firefox
sudo mkdir -p /usr/lib/firefox-addons/plugins/
sudo ln -s /usr/java/jreX.Y.Z.AAA/lib/i386/libnpjp2.so /usr/lib/firefox-addons/plugins/

Or, for 64-bit:

sudo ln -s /usr/java/jreX.Y.Z.AAA/lib/amd64/libnpjp2.so /usr/lib/firefox-addons/plugins/

Or, to find it by script:

find /usr/java -name "libnpjp*"
sudo ln -sv $(find /usr/java -name "libnpjp*" | tail -n 1) /usr/lib/firefox-addons/plugins/

Test: How do I test whether Java is working on my computer?
https://www.java.com/en/download/testjava.jsp

Or,

In Firefox, type about:plugins in the Location bar to confirm that the Java Plugin is loaded. 

---

How do I download and install 32-bit Java for Linux?
https://www.java.com/en/download/help/linux_install.xml#download

在 Ubuntu Linux 中啟用瀏覽器
http://www.java.com/zh_TW/download/help/enable_browser_ubuntu.xml

How to add java plugin for Firefox on Linux? - Stack Overflow
http://stackoverflow.com/questions/14491322/how-to-add-java-plugin-for-firefox-on-linux