There's one I'd really love to have in all Mozilla products, including Nvu: I want a special very visible message/tooltip/popup/whatever when I am about to fill in a type="password" form field, or an HTTP/FTP account/password HTTP popup, or when I enter my master password and when the CapsLock key is on. WindowsXP does it on its logon page, and it's a brilliant idea. I want that caps-lock warning in Mozilla products.

Update: filed under bug 259059.