Thanks for the suggestion. I downloaded the plug-in and tried it out a bit. I didn't realize that the package comes w/ DjVuViewer.exe, an executable that can be used without a web browser -- I had the opposite impression when looking at the name "Lizardtech Official DjVu Browser Plug-in
" and the system requirements (IE 5 or later, Mozilla 1.0 or later-based browser).
Unfortunately, the plug-in doesn't appear to be as portable as I like (e.g. it appears to modify file associations w/o asking) and I didn't succeed in getting DjVuViewer.exe to view a djvu file when I passed the name of a djvu file to it on the command line, so ATM I think I'll be continuing to evaluate other options.
(FWIW, I didn't start w/ IrfanView -- my initial testing was w/ WinDjView and djview (in DjVuLibre). Being able to comfortably use IrfanView might have been nice as that'd be one less thing to look after ("system administration"-wise). Perhaps this will be some additional incentive for my brain to rewire