Annoying issue with Opera and Zoho Mail which I think is likely an Opera setting somewhere, but have yet to find it!

What happens is that I open Zoho Mail in Opera and I continually get these pop-ups.

I seem to get one pop-up per wmsX.zoho.com where X = 1 to 9.

Any idea how to stop this? As I said it's probably an Opera setting, but where?