Resolved value doesn't really account for what should happen when you try to get the "width" value of an element that has box-sizing: border-box using getComputedStyle. 

The question of what should happen had been discussed with the previous editor: http://lists.w3.org/Archives/Public/www-style/2011Jun/0420.html

However, I believe the correct behavior is that getComputedStyle should return the round-trippable value for width and should be special cased. Currently, Webkit and Internet Explorer return the round trippable value, while Firefox returns the used value. 

When the value is not round-trippable, people view it as a bug, as is evidenced by this bug report in Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=520992

Furthermore, without the round-trippable value, you are forced to augment it by the border-width and padding values in order to get the correct round-trippable value. It has surfaced as a hurdle to completing this ticket and making border box save to use in jQuery as well: http://bugs.jquery.com/ticket/11004 . 

Also, Mozilla has stated they aren't prepared to drop the box-sizing prefix until they do the same in regards to getComputedStyle the same as Webkit and IE. Having the spec. specify what to do will help move this along.

The previous editor believed that special-casing this wasn't worth the effort, but it appears that special casing is already the behavior in all major browsers besides for Firefox.