I cant use any Java applets. I installed icedtea-7-plugin, and it is even activated under Add-Ons, but if I for example click:
www.java.com/de/download/testjava.jsp
The test-screen remains grey.
I definitely have a JRE installed--openjdk-7-jre and icedtea-7-plugin are both installed.
The output of java -version is:
java version "1.6.0_24"
OpenJDK Runtime Enviroment (IcedTea6 1.11.1) (6b24-1.11.1-4ubuntu3)
OpenJDK 64-Bit Server VM (build 20.0-b12, mixed mode)
I found the solution. In my privacy configuration I didn't allow Firefox to accept 3rd party cookies.
I dont have the slightest idea, why that is needed on the official Java site, but now it works!