The firewall rules are ok since I have a different server with the console working on port 5555. I really need to access the console from the web browser.
@Simon_Hanisch1 is already asking the right question. I have also see exactly the same behavior when someone accidently moved the UI ports to deny-by-default.
Ideally your port 5543 is still working fine, so you can login and fix it.
Alternatively you can also use command central to check and solve the problem.
You can try accessing through diagnostics port 9999. Check this document for details. If you can access through diagnostics port but not from 5543 or 5555, it is probably because your integration server is not responsive and/or under heavy load.
I also agree on previous comments. It is highly likely that it is configured to deny on some conditions. Check this settings from admin UI.