IE and Safari are little bit picky when it comes to passing and calculating dates using new Date, so for example this will not work on IE or Safari:
var date = new Date("2011-02-07");
because IE and Safari do not support this type of date format YYYY-MM-DD, to make it right here are the valid date formats that you can use:
var date = new Date(2011, 01, 07); // yyyy, mm-1, dd
var date = new Date(2011, 01, 07, 11, 05, 00); // yyyy, mm-1, dd, hh, mm, ss
var date = new Date("02/07/2011"); // "mm/dd/yyyy"
var date = new Date("02/07/2011 11:05:00"); // "mm/dd/yyyy hh:mm:ss"
var date = new Date(1297076700000); // milliseconds
var date = new Date("Mon Feb 07 2011 11:05:00 GMT"); // ""Day Mon dd yyyy hh:mm:ss GMT/UTC
more info you can find here:
http://biostall.com/javascript-new-date-returning-nan-in-ie-or-invalid-date-in-safari/