Click the 'Restore to Default' button in the Options dialog -> https://support.mozilla.com/en-US/kb/How%20to%20set%20the%20home%20page?s=set+home+page&r=0&as=s

(Or set your homepage to about:home)

What is an "Options dialog"? I don't see a "Restore to Default" button anywhere.

When I click on "Mozilla Firefox" icon on my desktop, I get a totally blank white screen.

I don't know how to set my homepage to about:home. I don't know where my homepage is.

Look at the top of the Firefox where it says File Edit View History Bookmarks Tools Help and click on the Tools ->Options ->General

If you have the Menu bar hidden and have a orange Firefox button then click on the an look to righe side of that menu where it says "Options"

If you want the Firefox start page as home page then set it as http://www.google.com/firefox/

When I click on the "Mozilla Firefox" icon on my desktop, I get a totally blank white screen. If I move the mouse pointer to the very top of the screen, a bar appears that says, "New tab."

There is nothing that says "File Edit View History Bookmarks Tools." There is no orange Firefox button.

I don't know how to set the Firefox start page as home page.

Sounds like you might be in Full Screen Mode - please hit the F11 key and see if the menus appear. You can then use F11 to go back to full screen mode

Hooray!!! I believe your F11 solution has cured my problem.

How in the world did you know about this little quirk?

It's well after midnight here and I must get to bed now. Tomorrow I'll see if everything's back to normal.