I have a website with a subdomain: test1.k12.hi.us and I am setting a cookie so that it can be accessed by subdomain: test2.k12.hi.us My code works on all modern versions of IE, Chrome, Safari and Firefox versions prior to 3.6.11. However, the cookie doesn't seem to get set properly in Firefox 3.6.11, 3.6.12 and the 4.0 beta with the same code. I am setting a session-lived cookie and specifying the domain as ".k12.hi.us". If I set the cookie domain as either "test1.k12.hi.us", "test2.k12.hi.us", the cookies are set but the cookies can't be shared between the subdomains. I would like to set the domain as ".k12.hi.us" so that I can't share the cookies between the two subdomains. Is there a bug in the Firefox 3.6.11 and later versions that prevents cookies being set properly in this manner? Your help would be appreciated. Thanks.