The button is meaningless, it is on any window. We really need an addon that, instead of closing the window, firefox throws it down (minimizes), so that the "close" button works just like "minimize". Old addons (Minimize to tray and "minimize when close, close tab (s) on Esc (Delete)") do not work! Please make such an addon.

Works as stated. One little niggle is that it doesn't have the "Are you sure you want to close this window" dialog which sis a little annoying