I have 2 s on my page, but one of them should have all of it elements disabled depending on some user\'s choice.
The fieldsets contain text
Why don't you just use:
$("#myfieldeset").attr("disabled", "disabled");
It worked for me. It disabled nicely all the children inputs.
EDIT: note thas the disabled attribute can be applied to fieldset element only in HTML5 (see merryprankster comment). Strangely enough, it does work with other browser than just Firefox and Opera, such as Chrome and Internet Explorer (tested IE7 and IE8).