I'm using Firefox 24.6 ESR to access several SE sites. Usually I log in at Tor.SE and then move to other sites. AskUbuntu shows a unique behaviour among other SE sites. So I visit the site and at some point decide to log in. So I click on the Login link and choose the correct link there. Now AU redirects me to the original page and does not show me as logged in. Only when I manually visit https://askubuntu.com/users/login I see the head and all other site visits are done as a logged in user. What can be the reason for this and how can this be resolved?