Gary, good news for my WMP plug-in problem and something the OP here might consider. On another forum I had pointed out this problem, to which someone had replied that he had the WMP plug-in installed and working.
Thus, I went back to look at what might have gone wrong with my install of the plug-in and solved the problem. It wasn't a mismatch in WMP versions after all.
Firefox was the first piece of software I installed to my freshly loaded Windows 7 x64 environment. I hadn't worked with x64 up until this install so I was not aware of MS's separation of "Program Files" and "Program Files (x86)" and the automatic defaulting of one folder or the other depending on the app being x64 or x86.
Thus, when I installed FF to my new Windows 7 environment I overrode the "Program Files (x86)" folder recommendation with the "Program Files" folder and installed there.
Apparently the Windows Media Player Firefox plug-in is hard-coded to accept the default install path that Windows passes it so it installed the plug-in all by its lonesome into "Program Files (x86)\Mozilla\Firefox\" (the last two folders being whatever the user chose as the install location).
When I found that lone plug-in directory there I simply moved all the WMP plug-in files over to the real FF location's plug-in folder and the WMP plug-in now works.