Very well, but need more functions Rated 4 out of 5 stars

Different alert box will cover each other, this should be fixed.

Lesser important notify, say, twitter or something, should disappeared after xxx milliseconds
Important notify should remains until close manually, if possible you can mark them with different (customizable) color
(my twitter app tab and Google reader keep popping and cover others, quiet annoying, while I still want to see the notify)

Close button should be easier to click, bigger one will be better

This review is for a previous version of the add-on ( 

Fair remarks. In fact among the new features of the ver. 1.1 you find auto-closing of the notifications customizable on a domain basis; in the next ver. I'll make the notifications nicer and with more accessible buttons and when I find the time I'd like to make them also "stackable", so that when there are more than one of them they will be all visible.
UPDATE 28/03/12: notifications vertically stacked has been introduced by the version 1.3