Solution:
Open a terminal (Application Menu/ Accessories/ Terminal) and type in:
sudo aptitude install sun-java6-jre sun-java6-plugin
or
sudo aptitude install sun-java5-jre sun-java5-plugin
Enter your password if prompted.
A license window will appear: Press TAB and then ENTER.
If a question is asked, answer "yes" (using the arrow keys and the ENTER key).
Conclusion:
You should now be able to run Java programs and see Java applets in the Firefox browser after restart Firefox.
