Mark that channel as anonymous in order to prevent any cookies
from being set here and potentially tie these proxied requests
to list updates which will not go through the proxy.
Also fix a return code in the case that httpChannel fails to QI.
MozReview-Commit-ID: BaRyYRlUbsB
--HG--
extra : rebase_source : 9ef4575553a7f4981c394b86e2923b5a5bf646c4