Firefox 15 should see changes to the border-image syn­tax to keep it in line with the latest ver­sion of the spec. There are four key changes: first, all of the indi­vidual border-image-* prop­er­ties are sup­por­ted. They are: border-image-source, border-image-slice, border-image-width, border-image-outset, and border-image-repeat. The border-image prop­erty is now a short­hand for all of those.

The second key change is that the centre of the image is not shown by default; in order to fill in the image, you have to use the fill keyword with border-image-slice, e.g.:

E { border-image-slice: 10 fill; }

Third, spe­cificity of the border prop­erty is now import­ant; if the border prop­erty is set to none and has higher spe­cificity, border-image won’t apply.

Fourth and finally, all of the prop­er­ties have been unprefixed.

The examples in Chapter 9 have been updated to reflect these changes. In Example 09–07 I’ve added an extra box to show the indi­vidual prop­er­ties, and also the fill keyword noted above.

— 20 July, 2012