How do I open table editor to edit specific cells?

I'm having problems editing a portion of the table.
I'm highlighting the cells, row or column.
I'm unable to open the table editor, using pointer and key command.
I'm trying all the key commands I can think of.
I can click the table editor in the menu bar but it only creates a new table.

Can someone confirm how I can open the editor or the key command I should use?

I'm on a MacBook Pro laptop OS 10.4.11, in Firefox.