Some features of Gemse are implemented using Java. If you do not need these features, you do not have to worry. However, if you want to use such a feature, you first have to do some preparations. The technology Gemse uses to call Java is called LiveConnect.
Since Gemse has to run the Java code with elevated permissions, Gemse itself must have full permissions. That means Gemse must run in the chrome, i.e. you have to install it as Firefox extension or XULRunner application.
You should use at least Firefox 3.6 or XULRunner 1.9.2 respectively.
You should install at least Java 6u17 from Sun and the Java plugin for Firefox that comes along with it. (If you use XULRunner you have to make it aware of the plugin. I do not know how one does that. Though, on my system it works out of the box.)
Older versions probably work as well. Therefore, if you don't like to update to the above versions, you should try with your older ones first. Be aware that you might run into weird bugs.
I am not aware of any other Java plugin that implements LiveConnect than the one from Sun.
Usually, the required libraries are shipped along with Gemse. If you want to update them, modify them, or if you checked out the git repository (which does not yet contain these libraries), you can read here where they are located.
If you use Gemse as Firefox extension, the
installation directory is located at extensions/Gemse@andonyar.com
in you profile directory. You can also start Gemse and enter the
command :help installation-directory&enter;. It prints the
location of the directory where Gemse is installed. (It fails with an
error, if Gemse does not run with full privileges.)
In Gemse's installation directory, you find a folder called
java. Gemse automatically loads all jar files of this
directory. Because it is sometimes easier to place a symbolic link to
a directory somewhere else, all subdirectories are scanned for jar
files as well. But jar files located in deeper folders are not
detected. Instead of jar files, class files can be placed there as
well, using the usual directory structure.
The NTNView makes use of the rendering architecture of JOMDoc. JOMDoc can be obtained from the JOMDoc download page. JOMDoc itself depends on a couple of additional libraries. Only those that are essential for Gemse are shipped along with it. Gemse's documentation contains a list of those libraries.