You must login into this network before you can access the internet.
This is the message that I see on the top of the screen on opening my browser. I can access the internet without 'log in' but when I click the 'open network login page' button, I get a success message from success.txt. Below are some (cropped) images.
This is about network detection done by Firefox on startup.
See Network Detection:
You can set network.captive-portal-service.enabled = false on the about:config page to disable this feature.
You can open the about:config page via the location/address bar. You can click the button to "Accept the Risk and Continue".
But, is this a bug? Why do I have to take risk and go to about:config? It works without login. It did not come just after update but a week after that.