Maybe it's different on nightly but for me the closed tab notification does not block anything. I can't speak for putting the new tab button to the top, but I

Maybe it's different on nightly but for me the closed tab notification does not block anything. I can't speak for putting the new tab button to the top, but I was asked if I want the URL bar at the bottom or top when installing Firefox for the first time. For me having the controls at the bottom is one of the killer features, because I can just use my thumb to do things.