EDIT: From mark.hch's answer I realised this is only a problem on Firefox. To clarify what I wrote below: I'm not asking for help with the event handler - that was just context. I specifically need the checkbox buttons to work on Firefox when holding the shift and CTRL keys.
I have a series of JQuery-UI checkboxes with an event handler set up and working properly. I want to be able to change the behaviour when a checkbox is clicked while the shift/CTRL buttons are pressed. The thing is, nothing actually happens when I click the checkboxes while holding them.
It looks to me like the buttons are being selected/highlighted rather than clicked. How can I stop this and register the click when the shift key is pressed?
For example: https://jsfiddle.net/51c72b20/
<script>
$(function() {
$( "#format" ).buttonset();
});
</script>
<div id="format">
<input type="checkbox" id="check1"><label for="check1">Alpha</label>
<input type="checkbox" id="check2"><label for="check2">Bravo</label>
<input type="checkbox" id="check3"><label for="check3">Charlie</label>
</div>