diff --git a/toolkit/components/url-classifier/tests/mochitest/chrome.ini b/toolkit/components/url-classifier/tests/mochitest/chrome.ini
index 5f8347787a10..7555ecef20e2 100644
--- a/toolkit/components/url-classifier/tests/mochitest/chrome.ini
+++ b/toolkit/components/url-classifier/tests/mochitest/chrome.ini
@@ -17,3 +17,4 @@ tags = trackingprotection
 tags = trackingprotection
 [test_trackingprotection_whitelist.html]
 tags = trackingprotection
+[test_donottrack.html]
diff --git a/toolkit/components/url-classifier/tests/mochitest/dnt.html b/toolkit/components/url-classifier/tests/mochitest/dnt.html
new file mode 100644
index 000000000000..effc3a4f8ce4
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/dnt.html
@@ -0,0 +1,31 @@
+<html>
+<head>
+<title></title>
+
+<script type="text/javascript">
+
+function makeXHR(url, callback) {
+  var xhr = new XMLHttpRequest();
+  xhr.open('GET', url, true);
+  xhr.onload = function() {
+    callback(xhr.response);
+  };
+  xhr.send();
+}
+
+function loaded(type) {
+  window.parent.postMessage("navigator.doNotTrack=" + navigator.doNotTrack, "*");
+
+  makeXHR("dnt.sjs", (res) => {
+    window.parent.postMessage("DNT=" + res, "*");
+    window.parent.postMessage("finish", "*");
+  });
+}
+
+</script>
+</head>
+
+<body onload="loaded('onload')">
+</body>
+
+</html>
diff --git a/toolkit/components/url-classifier/tests/mochitest/dnt.sjs b/toolkit/components/url-classifier/tests/mochitest/dnt.sjs
new file mode 100644
index 000000000000..bbb836482ada
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/dnt.sjs
@@ -0,0 +1,9 @@
+function handleRequest(request, response) {
+  var dnt = "unspecified";
+  if (request.hasHeader("DNT")) {
+    dnt = "1";
+  }
+
+  response.setHeader("Content-Type", "text/plain", false);
+  response.write(dnt);
+}
diff --git a/toolkit/components/url-classifier/tests/mochitest/mochitest.ini b/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
index f829c23a04ed..167a235bee96 100644
--- a/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
+++ b/toolkit/components/url-classifier/tests/mochitest/mochitest.ini
@@ -20,6 +20,8 @@ support-files =
   workerFrame.html
   ping.sjs
   basic.vtt
+  dnt.html
+  dnt.sjs
 
 [test_classifier.html]
 skip-if = (os == 'linux' && debug) #Bug 1199778
diff --git a/toolkit/components/url-classifier/tests/mochitest/test_donottrack.html b/toolkit/components/url-classifier/tests/mochitest/test_donottrack.html
new file mode 100644
index 000000000000..56003e7eb60d
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/test_donottrack.html
@@ -0,0 +1,150 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 1258033 - Fix the DNT loophole for tracking protection</title>
+  <script type="text/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+</head>
+
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+
+<script class="testbody" type="text/javascript">
+
+var Cc = SpecialPowers.Cc;
+var Ci = SpecialPowers.Ci;
+
+var mainWindow = window.QueryInterface(Ci.nsIInterfaceRequestor)
+                    .getInterface(Ci.nsIWebNavigation)
+                    .QueryInterface(Ci.nsIDocShellTreeItem)
+                    .rootTreeItem
+                    .QueryInterface(Ci.nsIInterfaceRequestor)
+                    .getInterface(Ci.nsIDOMWindow);
+
+const tests = [
+  // DNT turned on and TP turned off, DNT signal sent in both private browsing
+  // and normal mode.
+  {
+    setting:  {dntPref:true, tpPref:false, tppbPref:false, pbMode:true},
+    expected: {dnt: "1"},
+  },
+  {
+    setting:  {dntPref:true,  tpPref:false, tppbPref:false, pbMode:false},
+    expected: {dnt: "1"}
+  },
+  // DNT turned off and TP turned on globally, DNT signal sent in both private
+  // browsing and normal mode.
+  {
+    setting:  {dntPref:false, tpPref:true,  tppbPref:false, pbMode:true},
+    expected: {dnt: "1"}
+  },
+  {
+    setting:  {dntPref:false, tpPref:true,  tppbPref:false, pbMode:false},
+    expected: {dnt: "1"}
+  },
+  // DNT turned off and TP in Private Browsing only, DNT signal sent in private
+  // browsing mode only.
+  {
+    setting:  {dntPref:false, tpPref:false, tppbPref:true,  pbMode:true},
+    expected: {dnt: "1"}
+  },
+  {
+    setting:  {dntPref:false, tpPref:false, tppbPref:true,  pbMode:false},
+    expected: {dnt: "unspecified"}
+  },
+  // DNT turned off and TP turned off, DNT signal is never sent.
+  {
+    setting:  {dntPref:false, tpPref:false, tppbPref:false, pbMode:true},
+    expected: {dnt: "unspecified"}
+  },
+  {
+    setting:  {dntPref:false, tpPref:false, tppbPref:false, pbMode:false},
+    expected: {dnt: "unspecified"}
+  },
+]
+
+const DNT_PREF = 'privacy.donottrackheader.enabled';
+const TP_PREF = 'privacy.trackingprotection.enabled';
+const TP_PB_PREF = 'privacy.trackingprotection.pbmode.enabled';
+
+const contentPage =
+  "http://mochi.test:8888/tests/toolkit/components/url-classifier/tests/mochitest/dnt.html";
+
+Components.utils.import("resource://gre/modules/Services.jsm");
+
+function whenDelayedStartupFinished(aWindow, aCallback) {
+  Services.obs.addObserver(function observer(aSubject, aTopic) {
+    if (aWindow == aSubject) {
+      Services.obs.removeObserver(observer, aTopic);
+      setTimeout(aCallback, 0);
+    }
+  }, "browser-delayed-startup-finished", false);
+}
+
+function executeTest(test) {
+  SpecialPowers.pushPrefEnv({"set" : [
+   [DNT_PREF, test.setting.dntPref],
+   [TP_PREF, test.setting.tpPref],
+   [TP_PB_PREF, test.setting.tppbPref]
+  ]});
+
+  var win = mainWindow.OpenBrowserWindow({private: test.setting.pbMode});
+
+  return new Promise(function(resolve, reject) {
+    win.addEventListener("load", function onLoad() {
+      win.removeEventListener("load", onLoad, false);
+      whenDelayedStartupFinished(win, function() {
+        win.addEventListener("DOMContentLoaded", function onInnerLoad() {
+          if (win.content.location.href != contentPage) {
+            win.gBrowser.loadURI(contentPage);
+            return;
+          }
+
+          win.removeEventListener("DOMContentLoaded", onInnerLoad, true);
+
+          win.content.addEventListener('message', function (event) {
+            let [key, value] = event.data.split("=");
+            if (key == "finish") {
+              win.close();
+              resolve();
+            } else if (key == "navigator.doNotTrack") {
+              is(value, test.expected.dnt, "navigator.doNotTrack should be " + test.expected.dnt);
+            } else if (key == "DNT") {
+              let msg = test.expected.dnt == "1" ? "" : "not ";
+              is(value, test.expected.dnt, "DNT header should " + msg + "be sent");
+            } else {
+              ok(false, "unexpected message");
+            }
+          });
+        }, true);
+        SimpleTest.executeSoon(function() { win.gBrowser.loadURI(contentPage); });
+      });
+    }, true);
+  });
+}
+
+let loop = function loop(index) {
+  if (index >= tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  let test = tests[index];
+  let next = function next() {
+    loop(index + 1);
+  };
+  let result = executeTest(test);
+  result.then(next, next);
+};
+
+SimpleTest.waitForExplicitFinish();
+loop(0);
+
+</script>
+
+</pre>
+</body>
+</html>
