Analysis shows many files but 0 bytes to delete, and Cookies are not vanquished by CCleaner.
Checkmark is in place to delete Firefox Cookies, as it is for Adobe Flash. Where have I gone wrong?
Have you tried taking the tick out of 'only delete Windows temp files older than 24 hours' ?
I am accustomed to seeing Firefox cookies being reported as 0 bytes,
but they still go when cleaned and their data is removed with them and then can no longer be used by the sites that planted them.
I suggest you stipulate the version of CCleaner and also Windows, and whether 32 bit or 64 bit,
without which it may be difficult to reproduce the problem and fix any bug.
I unchecked the "24 hour" box and tried again. All but four Cookies (folders) were deleted. The next attempt removed two. Finally, on the third run all "Cookies to be deleted" were gone.
Version 1750 (64-bit) on Windows 8 PV edition.