I wish I could title this better. An example seems the best way of making the point: In icedove>preferences>attachments, for 'JEPG image' one can select 'Image Viewer' or 'Use other ...'. It turns out that 'Image Viewer' is actually '/usr/bin/eog' on my system. I only know that because after opening eog on the command line, clicking on 'Help>About', I see "Image Viewer" ... "The GNOME image viewer". It gives you no clue as to what the actual binary is, so, when the program is opened 'via' it's 'Image Viewer' name in icedove, how in heck would you figure out what the actual binary is? Is there some table somewhere, or some list of associations or something? The above is just one example--this problem exists in all GUIs all the time. It's a sad example of Linux trying hard to be as stupid and unhelpful as Windows :-(