Thank you very much.
The first suggestion (but not the second) did the deed :D.
The second suggestion effects another change:
It removes the "Glassfish News" node (in the tree on the left), and
it removes the bottom frame.
In fact, the two suggestions complement each other well.
I later found another thread by Anissa suggesting to remove modules/console-updatecenter-plugin.jar that will altogether remove "Update Center" from Glassfish Admin Console. This could be THE solution for installs with no Internet access.
Thanks,
Opher.
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