I have spoken to one of the Internet Helpdesk Agents (they are so great - and if they don't know the answer they go out of the way to find it!) and they told me that BA only test the web systems on IE as that is the only system that they have, the Internet helpdesk have one copy of NN that they can use to test ba.com but that's it, and if you're on a Mac then ouch!

I was told that the seat change unavailable message appears when there are a large number of Silver and Gold card holders on a flight, and is only supposed to show to Blue Card holders, but that there's a bug in the system that means that it hits everyone, the person I spoke to didn't know how long it would take until it was sorted.

Hope that this helps a little!

Worthless