I cannot log into Contao with Internet Explorer, but only with Firefox.
This issue occurres if the the system time on either the live server or your local computer is incorrect. Whereas Firefox is able to synchronize the client and server time and set the correct expiration date of the authentication cookie, Internet Explorer seems to simply rely on the server time. So if the server time is more than 5 minutes behind, you will not be able to log into Contao.
To fix this issue, set the correct server time on both the server and your local computer.
Last update on 2019-04-12 by Leo Feyer.