Firefox Java Plugin — Debian Wheezy

By default Firefox has no Java plugin because of security issues.
One can install plugin by following next steps:
0. Exit Firefox browser if it is running
1. Make directory if it does not exist -> /usr/lib/mozilla/plugins
2. Make a symbolic link for libnpjp2.so file which resides in JRE directory, e.g.:

sudo ln -s /usr/lib/jvm/jdk1.8.0_20/jre/lib/amd64/libnpjp2.so /usr/lib/mozilla/plugins/libnpjp2.so

Please note, that amd64 is an architecture of the OS you have installed, possibly it could be i386 in your case.
3. Start Firefox and type about:plugins in address box to check if browser able to see Java plugin.

Install proprietary Oracle JDK in Debian 7.0 Wheezy

This is a YAP (yet another post) about how one can manually install Oracle’s proprietary JDK/JRE version (in Debian 7.0 Wheezy as an example).

First of all, download fresh version of JDK/JRE from the Oracle website.
Copy archive to desired location, in the following example we will use

/usr/lib/jvm

as an installation source directory.
Unpack the archive and run next commands:

sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk/bin/java 1071
sudo update-alternatives --install /usr/bin/javac javac /media/mydisk/jdk/javac 1071
sudo update-alternatives --install /usr/bin/jcontrol jcontrol /media/mydisk/jdk/bin/jcontrol 1071

You may need read man pages for update-alternatives to check out the parameters and what they mean.

Now, if you want freshly installed version of java/javac to be default in your system, run next commands:

sudo update-alternatives --config java
sudo update-alternatives --config javac
sudo update-alternatives --config jcontrol

Follow the instructions issued by update-alternatives to select default version among the list of available installations.
After that, check if everything worked fine by issuing commands

java -version
javac -version

You should see 1.8.0 for both.