i see where the problem is...i dont know exactly what is causing it, but it has happened to me before...
after downloading the latest firefox, it didnt work, wouldnt connect to the internet and said the same thing you wrote above...it happened on a windows vista home premium and a windows xp...but my other windows vista home premium it worked...so im guessing its some firefox update they are trying to fix, and by latest, do you mean Firefox 3 Beta 5 or Firefox 4 (minefield?)
For both of those it happened...the only solutions i have found is using internet explore, (or downloading safari 3) or reinstalling the whole system...
as of yet, i dont know of any other solution...