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diff --git a/gfx/layers/apz/test/mochitest/helper_zoomed_pan.html b/gfx/layers/apz/test/mochitest/helper_zoomed_pan.html
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+++ b/gfx/layers/apz/test/mochitest/helper_zoomed_pan.html
@@ -0,0 +1,79 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <meta name="viewport" content="width=device-width; initial-scale=1.0,minimum-scale=1.0">
+  <title>Ensure layout viewport responds to panning while pinched</title>
+  <script type="application/javascript" src="apz_test_utils.js"></script>
+  <script type="application/javascript" src="apz_test_native_event_utils.js"></script>
+  <script src="/tests/SimpleTest/paint_listener.js"></script>
+  <style>
+    body {
+      margin: 0;
+      padding: 0;
+    }
+    #content {
+      height: 5000px;
+      width: 5000px;
+      background: repeating-linear-gradient(#EEE, #EEE 100px, #DDD 100px, #DDD 200px);
+    }
+  </style>
+</head>
+<body>
+  <div id="content"></div>
+  <script type="application/javascript">
+    const RESOLUTION = 4;
+    const OFFSET_SCREEN_PX = 50;
+    const OFFSET_CSS_PX = OFFSET_SCREEN_PX / RESOLUTION;
+
+    function computeDelta(visual) {
+      // Compute the distance from the right/bottom edge of the visual
+      // viewport to the same edge of the layout viewport and add the desired
+      // offset to that.
+      // We can ignore scrollbar width here since the scrollbar is layouted at
+      // the right/bottom edge of this content, not of this window in the case
+      // of containerful scrolling.
+      return visual - (visual / RESOLUTION) + OFFSET_CSS_PX;
+    }
+
+    async function test() {
+      const cases = [
+        {
+          x: 0,
+          y: 0,
+          dx: (width) => -computeDelta(width),
+          dy: (height) => 0,
+          expected: {
+            x: [OFFSET_CSS_PX, "x-offset was adjusted"],
+            y: [0, "y-offset was not affected"],
+          },
+        },
+        {
+          x: OFFSET_CSS_PX,
+          y: 0,
+          dx: (width) => 0,
+          dy: (height) => -computeDelta(height),
+          expected: {
+            x: [OFFSET_CSS_PX, "x-offset was not affected"],
+            y: [OFFSET_CSS_PX, "y-offset was adjusted"],
+          },
+        },
+      ];
+
+      for (let c of cases) {
+        await promiseNativeTouchDrag(window,
+                                     c.x,
+                                     c.y,
+                                     c.dx(document.documentElement.clientWidth),
+                                     c.dy(document.documentElement.clientHeight));
+        await promiseApzFlushedRepaints();
+        is(window.scrollX, c.expected.x[0], c.expected.x[1]);
+        is(window.scrollY, c.expected.y[0], c.expected.y[1]);
+      }
+    }
+
+    SpecialPowers.getDOMWindowUtils(window).setResolutionAndScaleTo(RESOLUTION);
+    waitUntilApzStable().then(test).then(subtestDone, subtestFailed);
+  </script>
+</body>
+</html>