I'm not sure where this belongs but posted it here as it affects FM in general. Came back to my computer one day after it had been in general use by the family. Found all the icons for FM files were different. All but one changed from the familiar blue file to a plain white box with black outline and in the lower left corner was the miniature version of the blue file. Another FM file (the only one on the desk top but closed) had the icon of one of my kids games. It still worked as the FM solution I expected but the icon is different. What happened? Any ideas about how to undo this?

Have you restarted? You may need to delete a bunch of caches, if you don't know where they are try one of the shareware cache cleaners (search www.macupdate.com lists for cache).