In Chrome and Safari, option tags inherit the disabled property their parent select. Therefore, $("select option:disabled"); returns ALL option tags if the select box is disabled, even though the disabled attribute of each option is not explicitly set. This is probably the desired behavior.
In FF 2-3.6, IE 6-8, and Opera 10, option tags do not inherit the disabled property.
Test case: http://jsfiddle.net/FBBYE/1/
Ticket: http://dev.jquery.com/ticket/6211