From time to time you may experience problems with the execution of the Java plugin in the Opera browser. This happens because its path is not correctly configured in the options.
To resolve the issue, open an Opera browser window and enter
into the URL bar. There should already be one path in the Plugin Path line. Enter a semicolon and add an additional path to the line. On a default Windows 7 and 8 installation, the Java plugin path should be
depending on your version of Java. Afterwards, scroll all the way down and save. Restart the browser the the issues should be solved.
Minecraft provides you with really good support on Linux. To be able to play, you need to download the .jar file from the official website first (you need that from the Minecraft for Linux / Other section: http://minecraft.net/download.
After you have it, you need to check if the java runtime environment is installed: open Synaptic Package Manager and search for the openjdk-7-jre package - if it isn't installed, install it now.
Head back to the downloaded minecraft.jar file. Right-click it and open the Properties. Go to the Permissions tab and check the Execute checkbox, close the window afterwards.
Now start minecraft by right-clicking the jar file again and selecting Open With >OpenJDK Java 7 Runtime - Enjoy Minecraft!