Demo page is broken

[RichardD2]

Your demo page is pulling in jQuery 1.9 from the Google CDN. As a result, once you've clicked on an element, you can no longer change its state. Elements which start closed can be opened once and never closed again; elements which start open can be closed once and never opened again.

This seems to be related to the changes around attr/prop handling:
http://jquery.com/upgrade-guide/1.9/#attr-versus-prop-

The following two changes seem to fix the problem:

Line 35: (toggleOpen)
Replace: var isOpen = typeof $details.attr('open') == 'string',
With: var isOpen = $details.prop('open'),

Line 125:
Add: $details.prop('open', typeof $details.attr('open') == 'string');
Before: toggleOpen($details, $detailsSummary, $detailsNotSummary);

[mathiasbynens]

Which browser are you testing this in? In IE 6 everything seems to work fine.

[RichardD2]

It's broken in Firefox 18.0.1, Opera 12.13 and IE9.
IE8 compatibility mode is even worse - you can't expand a collapsed element.
IE7 compatibility mode works fine.
Chrome supports the element natively, so it works as expected.

[mathiasbynens]

Should be fixed now. Thanks for reporting the issue and even providing a fix!