On server side? Apparantly not. On client side, you can use custom styles. Resizing the page can also help. If you zoom into the page, the element gets flattened to a top bar.
I use Stylus to activate this on demand. But zooming in will do the trick as well.
@-moz-document domain("itch.io") {
.user_tools {
position: static;
}
}
And on developer side, a banner over a web game can help.