preventDefault() not stopping default browser behavior for Ctrl-PgUp and Ctrl-PgDn

preventDefault() not stopping default browser behavior for Ctrl-PgUp and Ctrl-PgDn

I'm trying to implement WAI-ARIA keyboard controls for an accordion, and I'm stuck on getting Ctrl-PgUp and Ctrl-PgDn to work correctly.  I've written the code to handle the correct behavior for the accordion, but I can't stop certain browsers from continuing their default behavior of switching between browser tabs.

Both Firefox 3.6.4 and Chrome 5 insist of switching the browser tab, although Firefox still performs the scripted accordion behavior.  Chrome does not.  Safari 5 and IE 7 both behave correctly, and perform the accordion actions without switching browser tabs.

My code looks like this:

$(document).keydown(function(e) {
                var el = document.activeElement;
                switch (e.which) {
                    //other key commands go here
                    case 34:
                        //Ctrl+PgDn
                        if(e.ctrlKey && $(el).parents('#accordion').length > 0) {
                            e.preventDefault();
                            e.stopImmediatePropagation();
                            e.cancelBubble = true;
                            e.returnValue = false;
                            // do the accordion stuff
                        }
                        break;
                  }
}

It should check if the user has pressed Ctrl-PgDn and is focused within the accordion, and then cancel the browser's default behavior, but none of it works.  I started with just preventDefault(), but added the others as I became more and more frustrated.  Is there any solution to this?