For the upcoming Firefox 3.1 release a lot of work has been going into improving its CSS support (specifically, in relation to the CSS 3 specification).
One areas that have received solid implementations is that of border-image. This is a new CSS 3 module that makes the exact slicing of images (and their positioning around an element) quite easy.
CSS3's nth-child selector allows for lovely effects, and is especially useful for styling alternate rows of a table. While not yet widely supported in browsers, it promises to be very useful in the future.