The details element hasn't been implemented in latest stable build of Firefox...

The details element hasn't been implemented in latest stable build of Firefox yet. Therefore the focus state isn't present on the summary element.
I think we should commit this for now as it will be implemented as per the W3C standards for Firefox soon enough. I've tested it in stable builds of other major browsers and it is working as expected on all except Firefox and IE.

Ref:
http://caniuse.com/#feat=details
https://bugzilla.mozilla.org/show_bug.cgi?id=591737
http://www.w3.org/html/wg/drafts/html/master/interactive-elements.html#t...