I've finally found and installed (with considerable
help) the required plugin to activate Java in Mozilla.
Here's the strangeness that's left.
In my .mozilla/default/pref.js file, I must hand edit
the user_pref("security.enable_java", true) entry,
setting to true. The next time I run Mozilla, java
will in fact work (mostly, details will follow). But
when I exit Mozilla and re-examine the pref.js file,
the security.enable.java entry is missing entirely.
So next time I run Mozilla, Java doesn't work, and
won't till I hand edit the pref.js file again.
When working, I can load any of the JDK demo applets
and they work. The Yahoo chat applet even works. But
if I go, for example, to www.datek.com and try to open
an account, their applet won't work (it will work,
however, in my old Netscape 4.75).