This solution is using javascript to open a new window when a user clicks on your custom share button.
HTML:
<a href="#" onclick="share_fb('http://urlhere.com/test/55d7258b61707022e3050000');return false;" rel="nofollow" share_url="http://urlhere.com/test/55d7258b61707022e3050000" target="_blank">
//using fontawesome
<i class="uk-icon-facebook uk-float-left"></i>
Share
</a>
and in your javascript file. note window.open params are (url, dialogue title, width, height)
function share_fb(url) {
window.open('https://www.facebook.com/sharer/sharer.php?u='+url,'facebook-share-dialog',"width=626, height=436")
}