Connecting to public wifi hotspots

[JD]

Hi All,
Ubuntu 12.10.
Latest updates as of 2 weeks ago.
Lost access to internet at home and so, I finally decided
to take it to a public hotspot to update ubuntu.

When I click on the NetworkManager (henceforth NM), icon I select the SSID
that is open (usually, at&t wifi, or some other nearby hotspot
which is also open).

NM does indeed connect, sets up the default route and populates
/etc/resolv.conf and assigns an ip address to my wifi interface wlan0.

However, when I fire up Firefox, I expected it to take me to the local
shop's login  (accept these blah blah blah agreement...etc).
Well, firefox only fails! It does not seem to display that local provider's
login page, and gives me the error page.

When I boot into Win7, it connects to these spots without any problems.

So, anyone know what the secret trick is?