First, in Nautilus, navigate to wherever you extracted the mbforth.jar
file and right click on it. Select Properties and, on the Permissions
tab, click the "Allow executing file as program" box.

Then, you can right click on the mbforth.jar file and there should be an
option along the lines of "Open with OpenJDK Java 6 Runtime" - this
works on my PC.

Interestingly, firing up a terminal, cd-ing to where I have the
mbforth.jar file and typing "java mbforth.jar", which should also work,
throws an exception.

Still can't make Misty Beach Forth run in Kdenlive Ubuntu. Any suggestions.

I don't know a lot about Java. The Applet1.class is located here...

mbforth.jar/com/mistybeach/forth

Seems like some of the things the app needs are in other subdirectories where
Java can't locate them.

I have no idea which class I should try to get Java to open up on.

The code from the Misty Beach forth URL page that launches and works in Windows
is...

Applet


An applet version of Misty Beach Forth is embedded here. It may take
a little while to download as the applet is about 180 KB.

You need to enable Java to launch the Misty Beach Forth applet.