Browser blocked, now ebay messages blocked?

[stillconfused]

Yesterday when I tried to log into ebay I got a message saying that my browser wasn't allowing cookies. Now I hadn't changed anything, apart from my IP address from the night before. So I reset the "remember history" thing to allow cookies which were already keep in my history, again.
Now I could log in.
Later that night I tried to respond to a message from a buyer and it gave me the respond page but no window in which to write the message. So I assumed that this was because it was outside of an actual transaction that was the reason.
This morning I have a question from a buyer for an item that is ending today, and when I tried to respond, the same thing happened.
I contacted live help, didn't really want to but, they suggested I use IE, I said I didn't know how to so she suggested clearing my history and trying again. Nothing worked???????????
Am I being be blocked by ebay? or is there a problem with my browser, firefox by the way and the only thing I have changed recently is that I now have AVG installed instead of Avast.

I need to respond to their question, how can I do this?

Thanks for any help.

I've just downloaded Opera and I'm using it now. How secure is it for accessing ebay? Is there any add-ons I need to prevent ebay tracking?