Don't use -domain. Firefox sees the space and just drops the domain altogether. If you look at the cookie details, you'll see that the domain is not set.
Domain is used to allow cookies to be shared by more than one machine within one domain. E.G. www.example.org can set the example.org domain so media.example.org can use the same cookie. localhost doesn't have a valid domain so you'll have to settle for a host only cookie, which is what you will get from the non-standard -domain => " ".
I wrongly guessed that you were using domain to get around the IE bug. Sorry about the windows slander ;^)