My privacy setting are 'accept third party cookies' and I haven't changed this at all. However, since installing firefox more and more sites are telling me cookies are not enabled - but they are. This happens over time to EVERY firefox installation I have, no matter what machine its' on and no matter what OS - it starts fine gradually gets worse and worse rejecting more and more cookies! WHY!
A couple of more things: You should verify that cookies are permitted for the website. To do that, open the website and check cookie permissions in Tools > Page Info > Permissions.
Also, in case you are using a firewall, check if it is not blocking the cookies.
Now its back again - Facebook is the latest 'victim' and say cookies not enabled on your browser - did all the fixes and still won't let me in.
Well thats' interesting - even though cookies were enabled in the options menu - on this page they were blocked, but I was still having the same problem after allowing them! It only made a difference when I selected the allow for session option !