WYSIWIG Table Editor not working
Judging from the multi-colored icons in the toolbar, I think your might have an older version.
I found a client site with 2.53 installed and using the popup am able to change all properties except the columns and rows. If I right click in one of the table cells I have options there to manage columns and rows and that seems to work.
You might give the right-click method a try or consider upgrading, if possible.