diff --git a/custom-elements/reactions/HTMLElement.html b/custom-elements/reactions/HTMLElement.html
index 5fe422cdfc1df5..bd252282161b59 100644
--- a/custom-elements/reactions/HTMLElement.html
+++ b/custom-elements/reactions/HTMLElement.html
@@ -28,12 +28,9 @@
     customElement.parentNode.innerText = '';
 }, 'innerText on HTMLElement');
 
-if ('outerText' in HTMLElement.prototype) {
-    // Not yet to be in the standard but all but Gecko supports this property: https://github.com/whatwg/html/issues/668
-    testNodeDisconnector(function (customElement) {
-        customElement.outerText = '';
-    }, 'outerText on HTMLElement');
-}
+testNodeDisconnector(function (customElement) {
+    customElement.outerText = '';
+}, 'outerText on HTMLElement');
 
 </script>
 </body>
diff --git a/html/dom/elements/the-innertext-idl-attribute/dynamic-getter.html b/html/dom/elements/the-innertext-and-outertext-properties/dynamic-getter.html
similarity index 93%
rename from html/dom/elements/the-innertext-idl-attribute/dynamic-getter.html
rename to html/dom/elements/the-innertext-and-outertext-properties/dynamic-getter.html
index b3e96f94a80501..e34fcf5ac1e444 100644
--- a/html/dom/elements/the-innertext-idl-attribute/dynamic-getter.html
+++ b/html/dom/elements/the-innertext-and-outertext-properties/dynamic-getter.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<title>innerText getter test with dynamic style changes</title>
+<title>innerText/outerText getter test with dynamic style changes</title>
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <div id="container"></div>
@@ -19,7 +19,8 @@
     if (!e) {
       e = container.firstChild;
     }
-    assert_equals(e.innerText, expectedPlain);
+    assert_equals(e.innerText, expectedPlain, "innerText");
+    assert_equals(e.outerText, expectedPlain, "outerText");
     container.textContext = '';
   }, msg + ' (' + format_value(html) + ')');
 }
diff --git a/html/dom/elements/the-innertext-idl-attribute/getter-first-letter-marker-multicol.html b/html/dom/elements/the-innertext-and-outertext-properties/getter-first-letter-marker-multicol.html
similarity index 69%
rename from html/dom/elements/the-innertext-idl-attribute/getter-first-letter-marker-multicol.html
rename to html/dom/elements/the-innertext-and-outertext-properties/getter-first-letter-marker-multicol.html
index 77a815c5410aac..3b579dca1c5e4d 100644
--- a/html/dom/elements/the-innertext-idl-attribute/getter-first-letter-marker-multicol.html
+++ b/html/dom/elements/the-innertext-and-outertext-properties/getter-first-letter-marker-multicol.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<title>Test innerText for a combination of a list item with ::first-letter in multicol</title>
+<title>Test innerText/outerText for a combination of a list item with ::first-letter in multicol</title>
 <link rel="help" href="https://html.spec.whatwg.org/multipage/dom.html#dom-innertext">
 <link rel="help" href="https://crbug.com/1174985">
 <script src="/resources/testharness.js"></script>
@@ -12,6 +12,7 @@
 <div id="item" class="col"><div class="col">PASS</div></div>
 <script>
   test(() => {
-    assert_equals(item.innerText, "PASS");
+    assert_equals(item.innerText, "PASS", "innerText");
+    assert_equals(item.outerText, "PASS", "outerText");
   }, "");
 </script>
diff --git a/html/dom/elements/the-innertext-idl-attribute/getter-tests.js b/html/dom/elements/the-innertext-and-outertext-properties/getter-tests.js
similarity index 100%
rename from html/dom/elements/the-innertext-idl-attribute/getter-tests.js
rename to html/dom/elements/the-innertext-and-outertext-properties/getter-tests.js
diff --git a/html/dom/elements/the-innertext-idl-attribute/getter.html b/html/dom/elements/the-innertext-and-outertext-properties/getter.html
similarity index 92%
rename from html/dom/elements/the-innertext-idl-attribute/getter.html
rename to html/dom/elements/the-innertext-and-outertext-properties/getter.html
index c84bb04a2f4740..ffb3d34fe94143 100644
--- a/html/dom/elements/the-innertext-idl-attribute/getter.html
+++ b/html/dom/elements/the-innertext-and-outertext-properties/getter.html
@@ -1,5 +1,5 @@
 <!DOCTYPE html>
-<title>innerText getter test</title>
+<title>innerText/outerText getter test</title>
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <style>
@@ -55,7 +55,8 @@
     while (e && e.nodeType != Node.ELEMENT_NODE) {
       e = e.nextSibling;
     }
-    assert_equals(e.innerText, expectedPlain);
+    assert_equals(e.innerText, expectedPlain, "innerText");
+    assert_equals(e.outerText, expectedPlain, "outerText");
     cont.textContent = '';
   }, msg + ' (' + format_value(html) + ')');
 }
diff --git a/html/dom/elements/the-innertext-idl-attribute/setter-tests.js b/html/dom/elements/the-innertext-and-outertext-properties/innertext-setter-tests.js
similarity index 100%
rename from html/dom/elements/the-innertext-idl-attribute/setter-tests.js
rename to html/dom/elements/the-innertext-and-outertext-properties/innertext-setter-tests.js
diff --git a/html/dom/elements/the-innertext-idl-attribute/setter.html b/html/dom/elements/the-innertext-and-outertext-properties/innertext-setter.html
similarity index 98%
rename from html/dom/elements/the-innertext-idl-attribute/setter.html
rename to html/dom/elements/the-innertext-and-outertext-properties/innertext-setter.html
index 0b8d5686743494..a835a164ed6353 100644
--- a/html/dom/elements/the-innertext-idl-attribute/setter.html
+++ b/html/dom/elements/the-innertext-and-outertext-properties/innertext-setter.html
@@ -85,4 +85,4 @@
   }, msg + ", detached");
 }
 </script>
-<script src="setter-tests.js"></script>
+<script src="innertext-setter-tests.js"></script>
diff --git a/html/dom/elements/the-innertext-idl-attribute/multiple-text-nodes.window.js b/html/dom/elements/the-innertext-and-outertext-properties/multiple-text-nodes.window.js
similarity index 80%
rename from html/dom/elements/the-innertext-idl-attribute/multiple-text-nodes.window.js
rename to html/dom/elements/the-innertext-and-outertext-properties/multiple-text-nodes.window.js
index 3d504b682e5c03..07c55e96693392 100644
--- a/html/dom/elements/the-innertext-idl-attribute/multiple-text-nodes.window.js
+++ b/html/dom/elements/the-innertext-and-outertext-properties/multiple-text-nodes.window.js
@@ -9,7 +9,8 @@ async_test(t => {
     t1.data = "X";
     t2.data = " ";
     t3.data = "Y";
-    assert_equals(div.innerText, "X Y");
+    assert_equals(div.innerText, "X Y", "innerText");
+    assert_equals(div.outerText, "X Y", "outerText");
     t.done();
   }, 100);
 }, "Ensure multiple text nodes get rendered properly");
diff --git a/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.html b/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.html
new file mode 100644
index 00000000000000..6500931a8411ba
--- /dev/null
+++ b/html/dom/elements/the-innertext-and-outertext-properties/outertext-setter.html
@@ -0,0 +1,140 @@
+<!DOCTYPE html>
+<title>outerText setter test</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<ul>
+  <li>A <span id="testReplacePrevious">B</span></li>
+  <li><span id="testReplaceFollowing">A</span> B</li>
+  <li>A <span id="testReplaceBoth">B</span> C</li>
+  <li><span id="testRemove">Testing</span> removing node using outerText.</li>
+</ul>
+
+<div id="container"></div>
+
+<script>
+"use strict";
+
+test(() => {
+  const node = document.getElementById("testReplacePrevious");
+  const parent = node.parentNode;
+
+  node.outerText = "Replaced";
+
+  assert_equals(parent.innerHTML, "A Replaced");
+  assert_equals(parent.childNodes.length, 1, "It got merged with the previous text node");
+}, "Replacing a node and merging with the previous text node");
+
+test(() => {
+  const node = document.getElementById("testReplaceFollowing");
+  const parent = node.parentNode;
+
+  node.outerText = "Replaced";
+
+  assert_equals(parent.innerHTML, "Replaced B");
+  assert_equals(parent.childNodes.length, 1, "It got merged with the following text node");
+}, "Replacing a node and merging with the following text node");
+
+test(() => {
+  const node = document.getElementById("testReplaceBoth");
+  const parent = node.parentNode;
+
+  node.outerText = "Replaced";
+
+  assert_equals(parent.innerHTML, "A Replaced C");
+  assert_equals(parent.childNodes.length, 1, "It got merged with the previous and following text node");
+}, "Replacing a node and merging with the previous and following text node");
+
+test(t => {
+  const container = document.getElementById("container");
+  t.add_cleanup(() => { container.textContent = ""; });
+
+  container.append("A", "B", document.createElement("span"), "D", "E");
+  assert_equals(container.childNodes.length, 5, "Precondition check: five separate nodes");
+
+  const node = container.childNodes[2];
+  node.outerText = "Replaced";
+
+  assert_equals(container.innerHTML, "ABReplacedDE");
+  assert_equals(container.childNodes.length, 3, "It got merged with the previous and following text node");
+  assert_equals(container.childNodes[0].data, "A");
+  assert_equals(container.childNodes[1].data, "BReplacedD");
+  assert_equals(container.childNodes[2].data, "E");
+}, "Only merges with the previous and following text nodes, does not completely normalize");
+
+test(() => {
+  const node = document.getElementById("testRemove");
+  const parent = node.parentNode;
+
+  node.outerText = "";
+
+  assert_equals(parent.innerHTML, " removing node using outerText.");
+}, "Removing a node");
+
+test(() => {
+  const node = document.createElement("span");
+
+  assert_throws_dom("NoModificationAllowedError", () => { node.outerText = ""; });
+}, "Detached node");
+
+testText("<div>", "abc", "abc", "Simplest possible test");
+testHTML("<div>", "abc\ndef", "abc<br>def", "Newlines convert to <br> in non-white-space:pre elements");
+testHTML("<pre>", "abc\ndef", "abc<br>def", "Newlines convert to <br> in <pre> element");
+testHTML("<textarea>", "abc\ndef", "abc<br>def", "Newlines convert to <br> in <textarea> element");
+testHTML("<div style='white-space:pre'>", "abc\ndef", "abc<br>def", "Newlines convert to <br> in white-space:pre element");
+testHTML("<div>", "abc\rdef", "abc<br>def", "CRs convert to <br> in non-white-space:pre elements");
+testHTML("<pre>", "abc\rdef", "abc<br>def", "CRs convert to <br> in <pre> element");
+testHTML("<div>", "abc\r\ndef", "abc<br>def", "Newline/CR pair converts to <br> in non-white-space:pre element");
+testHTML("<div>", "abc\n\ndef", "abc<br><br>def", "Newline/newline pair converts to two <br>s in non-white-space:pre element");
+testHTML("<div>", "abc\r\rdef", "abc<br><br>def", "CR/CR pair converts to two <br>s in non-white-space:pre element");
+testHTML("<div style='white-space:pre'>", "abc\rdef", "abc<br>def", "CRs convert to <br> in white-space:pre element");
+testText("<div>", "abc<def", "abc<def", "< preserved");
+testText("<div>", "abc>def", "abc>def", "> preserved");
+testText("<div>", "abc&", "abc&", "& preserved");
+testText("<div>", "abc\"def", "abc\"def", "\" preserved");
+testText("<div>", "abc\'def", "abc\'def", "\' preserved");
+testHTML("<svg>", "abc", "<svg></svg>", "outerText not supported on SVG elements");
+testHTML("<math>", "abc", "<math></math>", "outerText not supported on MathML elements");
+testText("<div>", "abc\0def", "abc\0def", "Null characters preserved");
+testText("<div>", "abc\tdef", "abc\tdef", "Tabs preserved");
+testText("<div>", " abc", " abc", "Leading whitespace preserved");
+testText("<div>", "abc ", "abc ", "Trailing whitespace preserved");
+testText("<div>", "abc  def", "abc  def", "Whitespace not compressed");
+testText("<div>abc\n\n", "abc", "abc", "Existing text deleted");
+testText("<div><br>", "abc", "abc", "Existing <br> deleted");
+testHTML("<div>", "", "", "Assigning the empty string");
+testHTML("<div>", null, "", "Assigning null");
+testHTML("<div>", undefined, "undefined", "Assigning undefined");
+testHTML("<div>", "\rabc", "<br>abc", "Start with CR");
+testHTML("<div>", "\nabc", "<br>abc", "Start with LF");
+testHTML("<div>", "\r\nabc", "<br>abc", "Start with CRLF");
+testHTML("<div>", "abc\r", "abc<br>", "End with CR");
+testHTML("<div>", "abc\n", "abc<br>", "End with LF");
+testHTML("<div>", "abc\r\n", "abc<br>", "End with CRLF");
+
+function testText(startingHTML, outerText, expected, description) {
+  test(t => {
+    const container = document.getElementById("container");
+    t.add_cleanup(() => { container.textContent = ""; });
+
+    container.innerHTML = startingHTML;
+    const elementToReplace = container.firstElementChild;
+
+    elementToReplace.outerText = outerText;
+    assert_equals(container.textContent, expected);
+  }, description);
+}
+
+function testHTML(startingHTML, outerText, expected, description) {
+  test(t => {
+    const container = document.getElementById("container");
+    t.add_cleanup(() => { container.textContent = ""; });
+
+    container.innerHTML = startingHTML;
+    const elementToReplace = container.firstElementChild;
+
+    elementToReplace.outerText = outerText;
+    assert_equals(container.innerHTML, expected);
+  }, description);
+}
+</script>
