firefox/testing/web-platform/tests/css/css-flexbox/flexbox_object.html

<!DOCTYPE html>
<title>flexbox | object fallback as a flex item</title>
<link rel="author" href="http://opera.com" title="Opera Software">
<link rel="help"
	href="http://www.w3.org/TR/css-flexbox-1/#justify-content-property">
<link rel="match" href="flexbox_object-ref.html">
<style>
div {
	background: #ffcc00;
	justify-content: space-around;
	display: flex;
}
div>* {
	background: #3366cc;
	margin: 0;
}

object {
	overflow: clip;
}
</style>

<div>
	<object>this is supposed to be a flex item</object>
	<p>this is supposed to be a flex item</p>
</div>