palemoon-dev/platform/layout/reftests/svg/mask-opacity-01.svg

<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">
  <title>Testcase for the combination of mask, clipPath and opacity</title>
  <defs>
    <mask id="m1" maskContentUnits="objectBoundingBox" style="mask-type: alpha;">
      <rect width="1" height="1" style="stroke:#ffffff; fill: #ffffff; opacity: 0.5;" mask="url(#m2)"/>
    </mask>
    <mask id="m2" maskContentUnits="objectBoundingBox" style="mask-type: alpha;">
      <rect width="0.5" height="1" style="stroke:none; fill: #ffffff"/>
    </mask>
  </defs>
  <rect width="100" height="100" fill="blue" mask="url(#m1)"/>
</svg>