javascript - TypeError: a is null - Firefox -

$('#table25').on('click', '.buyable', function () {      var th = $(this);      var thclass = $(this).attr('class').split(' ')[1];      var td = $('#table25').find('td.'+thclass);      if ($('#checkuserstatus').val() == "0") {         $('#pleaslogin').modal('show');         return;      }      var prodtitle = $('#table25title').text();      var hex = rgbhex(td.css('background-color'));      if (hex != '#859de6') {         var y = '';         var x = '';         var xy = th.data('buyable');         var pageurl = document.url;         $.ajax({             url: '/prod_selected/',             type: 'get',             data: {title: prodtitle, xy: xy, x: x, y: y, pageurl: pageurl}         }).done(function (data) {             if (data != 'bad') {               $('#cart').text(data);               td.css('background-color', '#859de6');               td.css('color', '#ffffff');             }         });      }  }); 

this working in chrome, not in firefox, getting:

typeerror: null 

what missing? using latest jquery lib

i replaced jquery.min.js uncompressed one, see in line happenning error. it? how can fix this?