Behaviour of html4J presenters is inconsistent on different platforms. With Browser Presenter we can open a new Window from html like this:

<script>
function openSecondaryWindow() {
    return win2 = window.open('index_1.html', 'secondary', 'width=300,height=150');
}
</script>
<button onclick="openSecondaryWindow();">Open</button>

With JavaFX WebView Presenter the index_1.html will be opened in the same window replacing the existing content.