diff --git a/toolkit/components/antitracking/test/browser/browser.ini b/toolkit/components/antitracking/test/browser/browser.ini
index dd3b7556fe5a..ab5806005d0e 100644
--- a/toolkit/components/antitracking/test/browser/browser.ini
+++ b/toolkit/components/antitracking/test/browser/browser.ini
@@ -56,6 +56,8 @@ skip-if = (os == "win" && os_version == "6.1" && bits == 32 && !debug) # Bug 149
 skip-if = serviceworker_e10s
 [browser_permissionInPrivateWindows.js]
 skip-if = serviceworker_e10s
+[browser_referrerDefaultPolicy.js]
+support-files = referrer.sjs
 [browser_siteSpecificWorkArounds.js]
 [browser_subResources.js]
 skip-if = serviceworker_e10s
diff --git a/toolkit/components/antitracking/test/browser/browser_referrerDefaultPolicy.js b/toolkit/components/antitracking/test/browser/browser_referrerDefaultPolicy.js
new file mode 100644
index 000000000000..9f7cf8bfb561
--- /dev/null
+++ b/toolkit/components/antitracking/test/browser/browser_referrerDefaultPolicy.js
@@ -0,0 +1,119 @@
+const CHROME_BASE = "chrome://mochitests/content/browser/browser/base/content/test/general/";
+Services.scriptloader.loadSubScript(CHROME_BASE + "head.js", this);
+/* import-globals-from ../../../../../browser/base/content/test/general/head.js */
+
+async function testOnWindow(private, expectedReferrer) {
+  info("Creating a new " + (private ? "private" : "normal") + " window");
+  let win = await BrowserTestUtils.openNewBrowserWindow({private});
+  let browser = win.gBrowser;
+  let tab = browser.selectedTab;
+  let b = browser.getBrowserForTab(tab);
+  await promiseTabLoadEvent(tab, TEST_TOP_PAGE);
+
+  info("Loading tracking scripts and tracking images");
+  await ContentTask.spawn(b, null, async function() {
+    {
+      let src = content.document.createElement("script");
+      let p = new content.Promise(resolve => { src.onload = resolve; });
+      content.document.body.appendChild(src);
+      src.src = "https://tracking.example.org/browser/toolkit/components/antitracking/test/browser/referrer.sjs?what=script";
+      await p;
+    }
+
+    {
+      let img = content.document.createElement("img");
+      let p = new content.Promise(resolve => { img.onload = resolve; });
+      content.document.body.appendChild(img);
+      img.src = "https://tracking.example.org/browser/toolkit/components/antitracking/test/browser/referrer.sjs?what=image";
+      await p;
+    }
+  });
+
+  await fetch("https://tracking.example.org/browser/toolkit/components/antitracking/test/browser/referrer.sjs?result&what=image")
+    .then(r => r.text())
+    .then(text => {
+      is(text, expectedReferrer, "We sent the correct Referer header");
+    });
+
+  await fetch("https://tracking.example.org/browser/toolkit/components/antitracking/test/browser/referrer.sjs?result&what=script")
+    .then(r => r.text())
+    .then(text => {
+      is(text, expectedReferrer, "We sent the correct Referer header");
+    });
+
+  await BrowserTestUtils.closeWindow(win);
+}
+
+add_task(async function() {
+  info("Starting referrer default policy test");
+
+  await SpecialPowers.flushPrefEnv();
+  await SpecialPowers.pushPrefEnv({"set": [
+    ["browser.contentblocking.allowlist.annotations.enabled", true],
+    ["browser.contentblocking.allowlist.storage.enabled", true],
+    ["network.cookie.cookieBehavior", Ci.nsICookieService.BEHAVIOR_REJECT_TRACKER],
+    ["privacy.trackingprotection.enabled", false],
+    ["privacy.trackingprotection.pbmode.enabled", false],
+    ["privacy.trackingprotection.annotate_channels", true],
+  ]});
+
+  await UrlClassifierTestUtils.addTestTrackers();
+
+  // no-referrer-when-downgrade
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers", 3]]});
+  await testOnWindow(false, TEST_TOP_PAGE);
+
+  // strict-origin-when-cross-origin
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers", 2]]});
+  await testOnWindow(false, TEST_DOMAIN);
+
+  // same-origin
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers", 1]]});
+  await testOnWindow(false, "");
+
+  // no-referrer
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers", 0]]});
+  await testOnWindow(false, "");
+
+  // Reset the pref.
+  Services.prefs.clearUserPref("network.http.referer.defaultPolicy.trackers");
+
+  // no-referrer-when-downgrade
+  await SpecialPowers.pushPrefEnv({"set": [
+    // Set both prefs, because if we only set the trackers pref, then the PB
+    // mode default policy pref (2) would apply!
+    ["network.http.referer.defaultPolicy.pbmode", 3],
+    ["network.http.referer.defaultPolicy.trackers.pbmode", 3],
+  ]});
+  await testOnWindow(true, TEST_TOP_PAGE);
+
+  // strict-origin-when-cross-origin
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers.pbmode", 2]]});
+  await testOnWindow(true, TEST_DOMAIN);
+
+  // same-origin
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers.pbmode", 1]]});
+  await testOnWindow(true, "");
+
+  // no-referrer
+  await SpecialPowers.pushPrefEnv({"set":
+    [["network.http.referer.defaultPolicy.trackers.pbmode", 0]]});
+  await testOnWindow(true, "");
+
+  // Reset the pref.
+  Services.prefs.clearUserPref("network.http.referer.defaultPolicy.trackers.pbmode");
+});
+
+add_task(async function() {
+  info("Cleaning up.");
+  await new Promise(resolve => {
+    Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, value => resolve());
+  });
+});
+
diff --git a/toolkit/components/antitracking/test/browser/referrer.sjs b/toolkit/components/antitracking/test/browser/referrer.sjs
new file mode 100644
index 000000000000..7ad49f24bb96
--- /dev/null
+++ b/toolkit/components/antitracking/test/browser/referrer.sjs
@@ -0,0 +1,29 @@
+// A 1x1 PNG image.
+// Source: https://commons.wikimedia.org/wiki/File:1x1.png (Public Domain)
+const IMAGE = atob("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKAAAAA1BMVEUAA" +
+                   "ACnej3aAAAAAXRSTlMAQObYZgAAAApJREFUCNdjYAAAAAIAAeIhvDMAAAAASUVORK5CYII=");
+
+function handleRequest(aRequest, aResponse) {
+  aResponse.setStatusLine(aRequest.httpVersion, 200);
+
+  let key = aRequest.queryString.includes("what=script") ? "script" : "image";
+
+  if (aRequest.queryString.includes("result")) {
+    aResponse.write(getState(key));
+    setState(key, "");
+    return;
+  }
+
+  if (aRequest.hasHeader('Referer')) {
+    let referrer = aRequest.getHeader('Referer');
+    setState(key, referrer);
+  }
+
+  if (key == "script") {
+    aResponse.setHeader("Content-Type", "text/javascript", false);
+    aResponse.write("42;");
+  } else {
+    aResponse.setHeader("Content-Type", "image/png", false);
+    aResponse.write(IMAGE);
+  }
+}