Try this to see if it works:

Tools > Options > Applications

and Assign the program for Adobe Acrobat Documents.

Problem has now disappeared. Tools->applications->whatever now tells me that my reader is Adobe BUT the reader still LOOKS like Nuance. HOWEVER the elevator now works. Maybe the problem is intermittent. If it reappears I will be back.

I don't know about Nuance, but if it said "Adobe" in Applications, you are probably using Adobe. You can always go to Help > About to check what is it and the version.

Well, you'd be wrong. Help->About tells me I am using FireFox 4.0. I do not see where I can get the name/version/serial of the PDF reader when I open it in Firefox. At least that's the case with the Nuance reader. Not sure about Adobe Reader X. Oh, and the Nuance reader can be VERY finicky about where you click on the elevator--particularly if the document has a lot of pages, which makes the elevator really tiny. I think some programmer didn't do his homework on how to apply the elevator code.

I don't mean you click "Help" in Firefox, I mean after you open your pdf document, click "Help" there. What you did is getting the version of Firefox, not the program that opened your pdf document.

But the issue is which PDF reader opens in Firefox. If I open the Adobe reader by clicking on a PDF filename in Windows Explorer, I get the Adobe reader if I have specified it as the default PDF reader. I get the Nuance reader if I have specified it as the default PDF reader (or if I choose a PDF reader other than the default in the Open With context menu).

You can install this Firefox add-on of Adobe Reader X:

http://get.adobe.com/reader/?promoid=BUIGO

I "upgraded" from Firefox 3.6.<something> to Firefox 4.0 within the last week or 10 days.