>>> * Contextual menu is not supported yet.
>>> 
>>> I think that depending on a thing at mouse event (file, dir, or URL),
>>> choice of operation should be popped up.  When there is no suggestion,
>>> `Edit' menu should be popped up.  Also, by click on mode-line, buffer
>>> list should be popped up.
>>> 
>>> I am using a global minor mode `poplife-mode' that puts commands on
>>> mouse-3.  I attach a file with poplife-mode to show the idea.
>> 
>> Thanks, this is a good starting point for adding contextual menu.
>> I tried poplife-mode, and it pops up the menu on mouse-3,
>> but it seems only when there is the selection already,
>> i.e. it doesn't pop up the menu when nothing is selected.
>> Is this intended to work this way?

I fixed it and confirm with Emacs -Q.  Can you try again to see
the approach to start with?