I believe this is a browser alert, you should be able to disable it in your browser options, or at least I think you can.
Ok, well I couldn't find where you would disable them, but you should be able to select to mark it as opened to clear the alert.
Getting rid of it was easy, delete key, boom, gone. That's not the issue. The issue is actually its source... Never had such thing happen before and I really don't want stupid/meaningless "surveys" pesting me...
I don't know of any option in both OS 5 and 6 to block that as well and here we are back to square one...