After a fresh install of Magento 2.0.0.0-dev41 (checked out via git clone https://github.com/magento/magento2.git .) I am unable to log into the backend with Firefox 18.0.2. Chromium works fine, so does Opera or Midori. I'm using Ubuntu 12.04.
Each time I try to login another row is added to the database table core_session. So it looks like the session is never started, maybe this is a duplicate of #105 ?