Hello @harryghgim
hope that everything going fine with you
i do not know why it even work in firefox 
i tried to control the size of the content but i failed before check this
but i did the following and it work for both chrome and firefox
a[href^=“https”]::after {
content:“”;
background-image:url(“https://raw.githubusercontent.com/mdn/learning-area/master/css/styling-text/typesetting-a-homepage-start/external-link-52.png”);
background-position:right;
background-size: 10px 10px;
background-repeat: no-repeat;
padding-right:12px;
}
hope that help and have a nice day