Oops!
Crossed posts!
It's taken me a while to get used to 'Open in New Tab' being the first option, rather than the second, when I right-click on a link. I kept opening a new window, rather than a tab, because the order has been switched round.
However, despite several of my add-ons not functioning under Firefox 4, I generally like the improvements. (It could be worse. If Microsoft had been involved, any 'upgrade' would have been certain to make things much harder to use!).