I thought I would let interested peoples know that I have had some success using the native JavaFX charting stuff in Java 8 with MASON. You no longer need to have JFreeChart to build charts, although I haven't explored any interactivity modality with JavaFX, if it exists.
For the moment, this is just pumping data through a custom time series generator at the end of a run rather than using the MASON GUI. JFreeChart is more mature, has more features, and has some graph interactivity out of the box (like NetLogo).
Tony