Mozilla 1.6 for Win32: Opening graphics in a helper app?

In Netscape 4.x (at least since 4.5), if you had a helper app defined 
for the graphics formats that Netscape usually supports, clicking on a 
link to a graphic or right-clicking on a graphic in a rendered page and 
selecting "View Image" in the context menu opened the graphic in your 
specified helper app. Mozilla, however, seems to ignore the helper app 
entry and continues to open graphics in a browser window. In 
Preferences/Advanced/System, I have also unchecked all the graphics 
formats under "Windows should use Mozilla to open these file types." Is 
there something else I need to set? Does Mozilla support this feature? 
Is it a bug? Tks for your help,

Jeff