Most likely it’s the CSS – I see the same issue in Chrome which also uses webkit. Try specifying the CSS for both to be the same:
.blog-post .heading h1{
font-size: 20px;
padding: 0;
margin: 0px;
color: #fff;
}
.blog-post .heading h1 a{
font-size: 20px;
padding: 0;
margin: 0px;
color: #fff;
}
And in the Elements Types add div.heading h1
You should then see that in Elements to Replace where you can specify the style. That should fix it. Let me know if you need more detail.