Flash can be embedded in MozSwing, both as part of html and as an swf file itself.
Here's an example (you can tell it's running inside Swing by noticing the Swing draggable control on the left):
Here's an example of some Ruby code running in Java (using the Java JRuby implementation) that embedds and then controlling a simple flash application.
In the code below I've commented out the line that loads the from a file url using what in effect is a relative reference (normally file:// urls don't work with relative references). Currently communicating to a flash file loaded from the filesystem doesn't work.