DropDowns don't work in Firefox 17 when are inside a sortable ul.

How to Reproduce:

1.Download: http://jqueryui.com/resources/download/jquery-ui-1.9.2.custom.zip

2.Find the default example for sortable:

jquery-ui-1.9.2.custom\\development-bundle\\demos\\sortable\\default.html

3. Replace first li item to:

<li><select><option value="1">1</option><option value="2">2</option></select>Item 1</li>

(this is just to add a html select to the first item.)

4. The dropdown options will not appear(as if the dropdown is disabled).