I think there is an error in Kickstart.php code.
I'm trying to restore a file and getting error 500 from the server, but instead of showing the error, kickstart just freezes. After debuging with Firefox inspector I have realized this JS is the isseu:
error: function(Request, textStatus, errorThrown) { var message = '<strong>AJAX Loading Error</strong><br/>HTTP Status: '+Request.status+' ('+Request.statusText+')<br/>'; message = message + 'Internal status: '+textStatus+'<br/>'; message = message + 'XHR ReadyState: ' + Response.readyState + '<br/>'; message = message + 'Raw server response:<br/>'+Request.responseText;
Response is not defined and I think it should be Request.
Best.