Thanks for your help.
Clearing the Java cache did not help,
but updating to the last FireFox version
solved the problem :-)
Further problems arise but maybe to my own
Another question: Why is the Applet so slow
when running the "signed" version of jMol ? For example,
drawing the lines of my own docking box takes a long time
(several seconds), while using the Unsigned Applet is much much faster.