There is only one account on all 4 machines, just
the wife and I live here and I see no need for
separate accounts (unless she starts trying to
install stuff on her own, unlikely)

As far as I can see, all Java is installed exactly
the same on all machines. I have sun-java6-bin,
sun-java6-jre, sun-java6-plugin, java-common,
sun-java6-fonts and on them (I think I don't
need the -bin, right?)

The Firefox options, add-ons, and plugins are the same
on all machines. I'm not running any java blockers
and java plugin 1.6.0_14 is on all of them.

The only difference on the machine that has problems
is that Ubuntu is installed "inside" Windows, where
it's a clean Ubuntu only install on the other machines.
Can't see how that could affect it.

Java does work, the wife uses Facebook a lot and the
farm games use some pretty intense java, they work
fine. Can you tell what is is about the menu on that
web site that is failing? This has me baffled.