IIRC, P7 still adhered to the old Program files folder install which is now taboo due to the current Windows version(s).  Trying to access readable/writable content in that location will be blocked or interfered with by UAC.  If this is the case, you are better off relocating the P7 runtime to a different area away from the Program Files folder.  It sounds like Firefox not deleting your content but rendering them inaccessible.  Conduct a disc search for something you know the name of and see if you get a hit.