This is more of a puzzle than a problem:
Every time I start Firefox, a "Desktop" folder is created in my home folder (home/me/Desktop). I delete it, use Firefox, it comes back.
Am I sure it's Firefox?
I have a basic, default installation (Freya), which has been updated. The only changes I made were to remove Midori and add Firefox. I did some trial-and-error and it only happens (and always happens) after starting Firefox.
I could live with it, I suppose, but the voices in my head are anal-retentive and being all ocd fussy about it. ;-)