This ought to be a dup, but I can't find one. The notification bar slide-in/-out has often been chunky, but we did what we had to to get the effect we wanted. Now we have CSS transitions that ought to take a lot of this out of XBL. I suspect it might also make things smoother. I'm certain it will substantially simplify notification.xml. Is there any reason not to do this?

This works, but has this slightly ugly hack: newitem.style.marginTop = "-50px"; I couldn't get the actual height of the notification bar without screwing up the transition. It simplifies the code somewhat but not greatly. It does feel smoother.

minor cleanup

It's not critical for the initial negative margin to match the real height -- what's mostly relevant is that the transition ends smoothly.

When I run test_notification.xul with this patch, I get drawing problems as the notifications appear. None of the notifications are in colour and the text appears to overlap each other. Possibly, an issue with transparency.

-moz-transition is currently broken. (It wasn't when I wrote the patch.)