Install xul-ext-cookie-monster from Wheezy.

It was updated to a good enough version in there as part of a Wheezy
point-release, no need to track unstable.

config/chroot_apt/preferences

@@ -188,10 +188,6 @@ Package: libbarry0
 Pin: release o=Debian,a=stable
 Pin-Priority: 1010
 
-Package: xul-ext-cookie-monster
-Pin: release o=Debian,a=unstable
-Pin-Priority: 999
-
 Package: xul-ext-foxyproxy-standard
 Pin: release o=Debian,a=experimental
 Pin-Priority: 999