Clicking button 3 iconifies the window. If the buttons fill up the window so that some are out of view, the window names are abbreviated, and if necessary a scrollbar is created. Since this functions as an icon manager, you probably don't want fvwm to post icons. By default, tkgoodstuff will tell fvwm not to post icons. But this will affect only windows created after tkgoodstuff starts up.
All parameters are adjustable in the preferences manager.