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diff --git a/dom/workers/test/test_navigator_workers_hardwareConcurrency.html b/dom/workers/test/test_navigator_workers_hardwareConcurrency.html
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+++ b/dom/workers/test/test_navigator_workers_hardwareConcurrency.html
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+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for Navigator.hardwareConcurrency</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  "use strict";
+
+  SimpleTest.waitForExplicitFinish();
+
+  function getWorkerHardwareConcurrency(onmessage) {
+    var script = "postMessage(navigator.hardwareConcurrency)";
+    var url = URL.createObjectURL(new Blob([script]));
+    var w = new Worker(url);
+    w.onmessage = onmessage;
+  }
+
+  function resistFingerprinting(value) {
+    return SpecialPowers.pushPrefEnv({"set": [["privacy.resistFingerprinting", value]]});
+  }
+
+  getWorkerHardwareConcurrency(e => {
+    var x = e.data;
+    is(typeof x, "number", "hardwareConcurrency should be a number.");
+    ok(x > 0, "hardwareConcurrency should be greater than 0.");
+
+    resistFingerprinting(true).then(() => {
+      getWorkerHardwareConcurrency(msg => {
+        const y = msg.data;
+        ok(y === 2, "hardwareConcurrency should always be 2 when we're resisting fingerprinting.");
+
+        resistFingerprinting(false).then(() => {
+          getWorkerHardwareConcurrency(msg1 => {
+            const z = msg1.data;
+            ok(z === x, "hardwareConcurrency should be the same as before we were resisting fingerprinting.");
+
+            SimpleTest.finish();
+          });
+        });
+      });
+    });
+  });
+
+  </script>
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>