gecko-dev/gfx/webrender/tests/bug_166.html

<style>
  body {
    padding: 20px;
    background: rgb(65, 149, 250);
    //font-size: 200px;
  }
</style>

<div style="opacity: 0.999; color: white">FOOBAR</div>
<div style="opacity: 1.0; color: white">FOOBAR</div>