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diff --git a/testing/web-platform/tests/html/editing/editing-0/contenteditable/selection-in-contentEditable-at-turning-designMode-on-off.tentative.html b/testing/web-platform/tests/html/editing/editing-0/contenteditable/selection-in-contentEditable-at-turning-designMode-on-off.tentative.html
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+++ b/testing/web-platform/tests/html/editing/editing-0/contenteditable/selection-in-contentEditable-at-turning-designMode-on-off.tentative.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>selection in contenteditable should not be changed when designMode is turned on/off</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<iframe srcdoc="<body contenteditable>abc</body>"></iframe>
+<script>
+  const test_load = async_test("Selection in contenteditable shouldn't be reinitialized when changing designMode");
+  window.addEventListener("load", test_load.step_func_done(() => {
+    let iframe = document.querySelector("iframe");
+    let iframeSelection = iframe.contentDocument.getSelection();
+    iframe.focus();
+    iframeSelection.collapse(iframe.contentDocument.body, 1);
+    function summariseRange(range) {
+      if (!range) {
+        return "null";
+      }
+      return `(${range.startContainer.nodeName}, ${range.startOffset}) - (${range.endContainer.nodeName}, ${range.endOffset})`;
+    }
+    let maybeNormalizedRangeSummary = summariseRange(iframeSelection.getRangeAt(0));
+    assert_in_array(maybeNormalizedRangeSummary, ["(BODY, 1) - (BODY, 1)", "(#text, 3) - (#text, 3)"],
+                    "Selection collapsed at end of <body> can be either as-is or normalized to the end of the text node");
+    iframe.contentDocument.designMode = "on";
+    assert_equals(summariseRange(iframeSelection.getRangeAt(0)), maybeNormalizedRangeSummary,
+                  "Turning designMode on at load event shouldn't change selection in contenteditable");
+    iframe.contentDocument.designMode = "off";
+    assert_equals(summariseRange(iframeSelection.getRangeAt(0)), maybeNormalizedRangeSummary,
+                  "Turning designMode off at load event shouldn't change selection in contenteditable");
+  }));
+</script>