cookie in cookie less domain

I have set up a cdn for my site and I use it for css, js, and images.

The site serves only those files

My problem is that with the page speed plugin in firefox for my image requests I see a cookie

Cookie fc=fcVal=7985951017741594560

does any one know wher开发者_运维知识库e it comes from ?

Thanks

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Thanks Ben

I have cleared my cache and the cookie did not come back