How to prevent background scrolling when Bootstrap 3 modal open on mobile browsers?

See here: https://github.com/twbs/bootstrap/issues/7501

So try:

$('body').css('overflow','hidden');
$('body').css('position','fixed');

V3.0.0. should have fixed this issue. Do you use the latest version? If so post an issue on https://github.com/twbs/bootstrap/