This tab allows you to edit, delete or add grids that the viewer will recognize, and make available at the log in screen.
Secondly, you need the grid selector on the log in screen. If you do not see it, press Shift-Ctrl-G to activate it.
The fields below this are auto-populated and cannot be edited:
See this page for documentation on Firestorm 4.6.1 (40478) and earlier.