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diff --git a/layout/reftests/layers/pull-background-displayport-3.html b/layout/reftests/layers/pull-background-displayport-3.html
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+<!DOCTYPE html>
+<html lang="en" class="reftest-wait" reftest-async-scroll>
+<meta charset="utf-8">
+<title>Scrollboxes with non-uniform backgrounds should prevent their contents from pulling background colors, even if those contents start out above uniform backgrounds</title>
+
+<style>
+
+div {
+  min-height: 50px;
+  box-model: border-box;
+}
+
+.first, .second {
+  border: 1px solid blue;
+  margin: 50px 0;
+}
+
+.border {
+  border: 1px solid black;
+}
+
+.underlap {
+  border: 1px solid #088;
+  margin-left: 120px;
+  width: 80px;
+  margin-bottom: -30px;
+}
+
+.scrollable {
+  height: auto;
+  overflow: auto;
+}
+
+.scrollarea {
+  width: 5000px;
+  border: none;
+  padding: 10px 0 20px;
+  height: auto;
+}
+
+.scrolled {
+  margin-left: 220px;
+  width: 100px;
+  height: 100px;
+  border-color: red;
+}
+
+body {
+  margin: 0;
+  padding: 0 100px;
+  height: 3000px;
+}
+
+</style>
+
+<div class="first" reftest-assigned-layer="page-background">
+  <!--
+    This is just a regular box, it should end up in the page background layer.
+  -->
+</div>
+
+<div class="underlap">
+  <!--
+    This item intersects with the scrollable box and is positioned below
+    .scrolled, in z-order.
+  -->
+</div>
+
+<div class="scrollable border"
+     reftest-displayport-x="0" reftest-displayport-y="0"
+     reftest-displayport-w="2000" reftest-displayport-h="200">
+  <div class="scrollarea">
+    <div class="scrolled border reftest-no-paint">
+      <!--
+        This box starts out above solid white background, but it will move so
+        that it intersects .underlap, so it shouldn't pull up a background
+        color to begin with so that it doesn't need to invalidate.
+      -->
+    </div>
+  </div>
+</div>
+
+<div class="second" reftest-assigned-layer="page-background">
+  <!--
+    This should share a layer with .first and the page background.
+  -->
+</div>
+
+<script>
+
+var scrollable = document.querySelector(".scrollable");
+
+function doTest() {
+  scrollable.scrollLeft = 100;
+  document.documentElement.removeAttribute("class");
+}
+
+// Make .scrollable start out with active scrolling.
+scrollable.scrollLeft = 0;
+scrollable.scrollLeft = 10;
+document.addEventListener("MozReftestInvalidate", doTest, false);
+// setTimeout(doTest, 500);
+
+</script>