In Firefox, right-click on the modal dialog, select 'Inspect element', find
<div id="mc_embed_signup" style="">, right-click on it to select 'delete node'... Modal dialog is gone - you are in control of the rendering !
There was a black 'x' in the top right of the pop over for me. Are you using a script blocker or something that's preventing the button from loading?
Oh, thanks - that is why I didn't see the 'x'. Well, I just deleted the modal dialog from the DOM... No I'll have to add "mc_embed_signup" div to my adblock blacklist.
I can see the same thing and there is no button to close it.