Why can't I login anymore?
Thank you for explaining the reason.
please tell me, have you installed any plugins forcing HTTPS connections (like "HTTPS Everywhere", for example)? If you're using any ad- or script-blocking plugins, please try to add todoist.com on their whitelists.
Also, you can try to clear your browser cache and cookies and try to log in through this page: http://todoist.com/Users/showLogin