This solution is for JoomlArt T3-framework ( t3bs3_blank)
Add these lines to template t3bs3_blank/js/script.js:
<code>
(function($){
$(document).ready(function(){
$('button.logoutButton').click(function(){
$('form#logoutForm').submit();
})
});
})(jQuery);
</code>
and this to t3bs3_blank/ect/assets.xml first thing after <assets>
<code>
<scripts>
<file>js/script.js</file>
</scripts>
</code>
Thanks!