animate scroll not reason for not working in FF

animate scroll not reason for not working in FF

is $('body , html') and $('body' , 'html') two different things ?? because the below code does't work:

  1.  $('body' , 'html')
  2.         .animate({ scrollTop: ($(section_id).offset().top - $('.main-nav').height()) }, {
  3.             'duration': 500
  4.         });


but the works:

  1.  $('body , html')
  2.         .animate({ scrollTop: ($(section_id).offset().top - $('.main-nav').height()) }, {
  3.             'duration': 500
  4.         });