Well, I have to admit you've tried everything I can think of at the moment. It's an odd one, though, for sure, but, as Jacqui has written, I think if it was Firefox or IE, or your computer also, it wouldn't just be happening on this forum. You'ld have it on other sites and, if it was your computer, other programs and all sorts. Yuku is a very temperamental beast so it wouldn't surprise me if you found out it is Yuku. I won't give up thinking of what it could be, though. I'd like to know myself.