While your code looks like it would work (I tested it on my end, altering just the cookie domain), I generally debug my cookie problems by removing everything that is not essential to setting the cookie and one-by-one adding them back in. For example, try setting the cookie without declaring the expiration date, the domain or the path. Just set the name and value. Then test it with Mozilla and afterward use the Cookie Manager in Mozilla to see exactly what was set. Provided that works, then add in the expiration date, then the path, and finally the domain. The most common problem I see with cookie files occurs when messing with the domain attribute. One small mistake and the cookie will never be set because it won't allow you to set a cookie for another domain.

Hope that helps.