I love the annotation Beta features!
As a suggestions, It would be great to have Author, Year and Title showing in the title bar of the open tab. It seems there is plenty of space to put it. That way, you always know which paper you are looking at when you switch through several open tabs.
It already helps a little bit, to have it in the title tag mouse-over, as you have it now. The same info in the window itself would make a huge difference.