I have cookies turned on but my logins to this site and others that use cookies expire when I close the browser window. I don't think the cookies are set to expire in a short time because I have been logged into some of the sites for months with Firefox on my PC. Is anyone else having this problem?

I have a couple of sites (like Linkfilter.com and Salon.com) which seem to have cookie problems. I log on and it seems to work, but if I go to the next page or try to post the site asks me to log on again.

But other forum sites work just fine. There must be a difference but I have no idea what it is.