1. Firstly is there any way to tell the app which Browser launched the Java Web Start .jnlp file?
Don't think so. You don't need a broswer to launch a Java Web Start app, so I don't think there is any out-the-box method of doing this. Even if there were, I'm not sure how it would help solve your issue.
2. How can you launch Firefox or IE from a Java app? Is there any API available?
Runtime.exec(). Presuming you know where the user has installed their browser. And which browser it is.
3. Preferably I do not want to save the html file to disk. Can it be passed directly from the Java app to the Browser?
You can't use a browser to open a file that doesn't exist. Lots of Swing components render HTML though - could you not just use a one of them in your app?
[ January 25, 2007: Message edited by: Paul Sturrock ]