Almost any extension can be chosen to 'save to disk' instead of realtime performance.
But having the QT plugin in FF is hard to keep under control, so I fired it. This made things a lot smoother.
This player-GUI is making things harder too, because the songs are embedded in a flash dialog.
So no normal webpage R-click behaviour. The R-click in the flash comes with the option 'Download this track'.
If clicked, it takes some moments to download the complete track in the cache, before the Save as dialog pops up.
This appears to be only possible when the actual track is playing.
If track 6 is playing, or was the latest, then R-clicking on track 2 with 'Download this track' will not work.
It will save track 6 again.