Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

40 files changed, 4326 insertions, 0 deletions

diff --git a/browser/base/content/test/about/POSTSearchEngine.xml b/browser/base/content/test/about/POSTSearchEngine.xml
new file mode 100644
index 0000000000..f2f884cf51
--- /dev/null
+++ b/browser/base/content/test/about/POSTSearchEngine.xml
@@ -0,0 +1,6 @@
+<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
+  <ShortName>POST Search</ShortName>
+  <Url type="text/html" method="POST" template="http://mochi.test:8888/browser/browser/base/content/test/about/print_postdata.sjs">
+    <Param name="searchterms" value="{searchTerms}"/>
+  </Url>
+</OpenSearchDescription>
diff --git a/browser/base/content/test/about/browser.ini b/browser/base/content/test/about/browser.ini
new file mode 100644
index 0000000000..ce82ff8006
--- /dev/null
+++ b/browser/base/content/test/about/browser.ini
@@ -0,0 +1,59 @@
+[DEFAULT]
+support-files =
+  head.js
+  print_postdata.sjs
+  searchSuggestionEngine.sjs
+  searchSuggestionEngine.xml
+  slow_loading_page.sjs
+  POSTSearchEngine.xml
+  dummy_page.html
+
+[browser_aboutCertError.js]
+[browser_aboutCertError_clockSkew.js]
+[browser_aboutCertError_exception.js]
+[browser_aboutCertError_mitm.js]
+[browser_aboutCertError_noSubjectAltName.js]
+[browser_aboutCertError_offlineSupport.js]
+[browser_aboutCertError_telemetry.js]
+[browser_aboutDialog_distribution.js]
+[browser_aboutHome_search_POST.js]
+[browser_aboutHome_search_composing.js]
+[browser_aboutHome_search_searchbar.js]
+[browser_aboutHome_search_suggestion.js]
+skip-if =
+  os == "mac"
+  os == "linux" && (!debug || bits == 64)
+  os == 'win' && os_version == '10.0' && bits == 64 && !debug # Bug 1399648, bug 1402502
+[browser_aboutHome_search_telemetry.js]
+[browser_aboutNetError.js]
+[browser_aboutNetError_csp_iframe.js]
+https_first_disabled = true
+support-files =
+  iframe_page_csp.html
+  csp_iframe.sjs
+[browser_aboutNetError_native_fallback.js]
+skip-if =
+  socketprocess_networking
+[browser_aboutNetError_trr.js]
+skip-if =
+  socketprocess_networking
+[browser_aboutNetError_xfo_iframe.js]
+https_first_disabled = true
+support-files =
+  iframe_page_xfo.html
+  xfo_iframe.sjs
+[browser_aboutNewTab_bookmarksToolbar.js]
+[browser_aboutNewTab_bookmarksToolbarEmpty.js]
+skip-if = tsan # Bug 1676326, highly frequent on TSan
+[browser_aboutNewTab_bookmarksToolbarNewWindow.js]
+[browser_aboutNewTab_bookmarksToolbarPrefs.js]
+[browser_aboutStopReload.js]
+[browser_aboutSupport.js]
+skip-if =
+  os == 'linux' && bits == 64 && asan && !debug # Bug 1713368
+[browser_aboutSupport_newtab_security_state.js]
+[browser_aboutSupport_places.js]
+skip-if = os == 'android'
+[browser_bug435325.js]
+skip-if = verify && !debug && os == 'mac'
+[browser_bug633691.js]
diff --git a/browser/base/content/test/about/browser_aboutCertError.js b/browser/base/content/test/about/browser_aboutCertError.js
new file mode 100644
index 0000000000..7f1f8149fa
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError.js
@@ -0,0 +1,548 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// This is testing the aboutCertError page (Bug 1207107).
+
+const GOOD_PAGE = "https://example.com/";
+const GOOD_PAGE_2 = "https://example.org/";
+const BAD_CERT = "https://expired.example.com/";
+const UNKNOWN_ISSUER = "https://self-signed.example.com ";
+const BAD_STS_CERT =
+  "https://badchain.include-subdomains.pinning.example.com:443";
+const { TabStateFlusher } = ChromeUtils.importESModule(
+  "resource:///modules/sessionstore/TabStateFlusher.sys.mjs"
+);
+
+add_task(async function checkReturnToAboutHome() {
+  info(
+    "Loading a bad cert page directly and making sure 'return to previous page' goes to about:home"
+  );
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    is(browser.webNavigation.canGoBack, false, "!webNavigation.canGoBack");
+    is(
+      browser.webNavigation.canGoForward,
+      false,
+      "!webNavigation.canGoForward"
+    );
+
+    // Populate the shistory entries manually, since it happens asynchronously
+    // and the following tests will be too soon otherwise.
+    await TabStateFlusher.flush(browser);
+    let { entries } = JSON.parse(SessionStore.getTabState(tab));
+    is(entries.length, 1, "there is one shistory entry");
+
+    info("Clicking the go back button on about:certerror");
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+    let locationChangePromise = BrowserTestUtils.waitForLocationChange(
+      gBrowser,
+      "about:home"
+    );
+    await SpecialPowers.spawn(bc, [useFrame], async function (subFrame) {
+      let returnButton = content.document.getElementById("returnButton");
+      if (!subFrame) {
+        if (!Services.focus.focusedElement == returnButton) {
+          await ContentTaskUtils.waitForEvent(returnButton, "focus");
+        }
+        Assert.ok(true, "returnButton has focus");
+      }
+      // Note that going back to about:newtab might cause a process flip, if
+      // the browser is configured to run about:newtab in its own special
+      // content process.
+      returnButton.click();
+    });
+
+    await locationChangePromise;
+
+    is(browser.webNavigation.canGoBack, true, "webNavigation.canGoBack");
+    is(
+      browser.webNavigation.canGoForward,
+      false,
+      "!webNavigation.canGoForward"
+    );
+    is(gBrowser.currentURI.spec, "about:home", "Went back");
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkReturnToPreviousPage() {
+  info(
+    "Loading a bad cert page and making sure 'return to previous page' goes back"
+  );
+  for (let useFrame of [false, true]) {
+    let tab;
+    let browser;
+    if (useFrame) {
+      tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, GOOD_PAGE);
+      browser = tab.linkedBrowser;
+
+      BrowserTestUtils.loadURIString(browser, GOOD_PAGE_2);
+      await BrowserTestUtils.browserLoaded(browser, false, GOOD_PAGE_2);
+      await injectErrorPageFrame(tab, BAD_CERT);
+    } else {
+      tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, GOOD_PAGE);
+      browser = gBrowser.selectedBrowser;
+
+      info("Loading and waiting for the cert error");
+      let certErrorLoaded = BrowserTestUtils.waitForErrorPage(browser);
+      BrowserTestUtils.loadURIString(browser, BAD_CERT);
+      await certErrorLoaded;
+    }
+
+    is(browser.webNavigation.canGoBack, true, "webNavigation.canGoBack");
+    is(
+      browser.webNavigation.canGoForward,
+      false,
+      "!webNavigation.canGoForward"
+    );
+
+    // Populate the shistory entries manually, since it happens asynchronously
+    // and the following tests will be too soon otherwise.
+    await TabStateFlusher.flush(browser);
+    let { entries } = JSON.parse(SessionStore.getTabState(tab));
+    is(entries.length, 2, "there are two shistory entries");
+
+    info("Clicking the go back button on about:certerror");
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    let pageShownPromise = BrowserTestUtils.waitForContentEvent(
+      browser,
+      "pageshow",
+      true
+    );
+    await SpecialPowers.spawn(bc, [useFrame], async function (subFrame) {
+      let returnButton = content.document.getElementById("returnButton");
+      returnButton.click();
+    });
+    await pageShownPromise;
+
+    is(browser.webNavigation.canGoBack, false, "!webNavigation.canGoBack");
+    is(browser.webNavigation.canGoForward, true, "webNavigation.canGoForward");
+    is(gBrowser.currentURI.spec, GOOD_PAGE, "Went back");
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+// This checks that the appinfo.appBuildID starts with a date string,
+// which is required for the misconfigured system time check.
+add_task(async function checkAppBuildIDIsDate() {
+  let appBuildID = Services.appinfo.appBuildID;
+  let year = parseInt(appBuildID.substr(0, 4), 10);
+  let month = parseInt(appBuildID.substr(4, 2), 10);
+  let day = parseInt(appBuildID.substr(6, 2), 10);
+
+  ok(year >= 2016 && year <= 2100, "appBuildID contains a valid year");
+  ok(month >= 1 && month <= 12, "appBuildID contains a valid month");
+  ok(day >= 1 && day <= 31, "appBuildID contains a valid day");
+});
+
+add_task(async function checkAdvancedDetails() {
+  info(
+    "Loading a bad cert page and verifying the main error and advanced details section"
+  );
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    let message = await SpecialPowers.spawn(bc, [], async function () {
+      let doc = content.document;
+
+      const shortDesc = doc.getElementById("errorShortDesc");
+      const sdArgs = JSON.parse(shortDesc.dataset.l10nArgs);
+      is(
+        sdArgs.hostname,
+        "expired.example.com",
+        "Should list hostname in error message."
+      );
+
+      Assert.ok(
+        doc.getElementById("certificateErrorDebugInformation").hidden,
+        "Debug info is initially hidden"
+      );
+
+      let exceptionButton = doc.getElementById("exceptionDialogButton");
+      Assert.ok(
+        !exceptionButton.disabled,
+        "Exception button is not disabled by default."
+      );
+
+      let advancedButton = doc.getElementById("advancedButton");
+      advancedButton.click();
+
+      // Wait until fluent sets the errorCode inner text.
+      let errorCode;
+      await ContentTaskUtils.waitForCondition(() => {
+        errorCode = doc.getElementById("errorCode");
+        return errorCode && errorCode.textContent != "";
+      }, "error code has been set inside the advanced button panel");
+
+      return { textContent: errorCode.textContent, tagName: errorCode.tagName };
+    });
+    is(
+      message.textContent,
+      "SEC_ERROR_EXPIRED_CERTIFICATE",
+      "Correct error message found"
+    );
+    is(message.tagName, "a", "Error message is a link");
+
+    message = await SpecialPowers.spawn(bc, [], async function () {
+      let doc = content.document;
+      let errorCode = doc.getElementById("errorCode");
+      errorCode.click();
+      let div = doc.getElementById("certificateErrorDebugInformation");
+      let text = doc.getElementById("certificateErrorText");
+      Assert.ok(
+        content.getComputedStyle(div).display !== "none",
+        "Debug information is visible"
+      );
+      let failedCertChain =
+        content.docShell.failedChannel.securityInfo.failedCertChain.map(cert =>
+          cert.getBase64DERString()
+        );
+      return {
+        divDisplay: content.getComputedStyle(div).display,
+        text: text.textContent,
+        failedCertChain,
+      };
+    });
+    isnot(message.divDisplay, "none", "Debug information is visible");
+    ok(message.text.includes(BAD_CERT), "Correct URL found");
+    ok(
+      message.text.includes("Certificate has expired"),
+      "Correct error message found"
+    );
+    ok(
+      message.text.includes("HTTP Strict Transport Security: false"),
+      "Correct HSTS value found"
+    );
+    ok(
+      message.text.includes("HTTP Public Key Pinning: false"),
+      "Correct HPKP value found"
+    );
+    let certChain = getCertChainAsString(message.failedCertChain);
+    ok(message.text.includes(certChain), "Found certificate chain");
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkAdvancedDetailsForHSTS() {
+  info(
+    "Loading a bad STS cert page and verifying the advanced details section"
+  );
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_STS_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    let message = await SpecialPowers.spawn(bc, [], async function () {
+      let doc = content.document;
+      let advancedButton = doc.getElementById("advancedButton");
+      advancedButton.click();
+
+      // Wait until fluent sets the errorCode inner text.
+      let ec;
+      await ContentTaskUtils.waitForCondition(() => {
+        ec = doc.getElementById("errorCode");
+        return ec.textContent != "";
+      }, "error code has been set inside the advanced button panel");
+
+      let cdl = doc.getElementById("cert_domain_link");
+      return {
+        ecTextContent: ec.textContent,
+        ecTagName: ec.tagName,
+        cdlTextContent: cdl.textContent,
+        cdlTagName: cdl.tagName,
+      };
+    });
+
+    const badStsUri = Services.io.newURI(BAD_STS_CERT);
+    is(
+      message.ecTextContent,
+      "SSL_ERROR_BAD_CERT_DOMAIN",
+      "Correct error message found"
+    );
+    is(message.ecTagName, "a", "Error message is a link");
+    const url = badStsUri.prePath.slice(badStsUri.prePath.indexOf(".") + 1);
+    is(message.cdlTextContent, url, "Correct cert_domain_link contents found");
+    is(message.cdlTagName, "a", "cert_domain_link is a link");
+
+    message = await SpecialPowers.spawn(bc, [], async function () {
+      let doc = content.document;
+      let errorCode = doc.getElementById("errorCode");
+      errorCode.click();
+      let div = doc.getElementById("certificateErrorDebugInformation");
+      let text = doc.getElementById("certificateErrorText");
+      let failedCertChain =
+        content.docShell.failedChannel.securityInfo.failedCertChain.map(cert =>
+          cert.getBase64DERString()
+        );
+      return {
+        divDisplay: content.getComputedStyle(div).display,
+        text: text.textContent,
+        failedCertChain,
+      };
+    });
+    isnot(message.divDisplay, "none", "Debug information is visible");
+    ok(message.text.includes(badStsUri.spec), "Correct URL found");
+    ok(
+      message.text.includes(
+        "requested domain name does not match the server\u2019s certificate"
+      ),
+      "Correct error message found"
+    );
+    ok(
+      message.text.includes("HTTP Strict Transport Security: false"),
+      "Correct HSTS value found"
+    );
+    ok(
+      message.text.includes("HTTP Public Key Pinning: true"),
+      "Correct HPKP value found"
+    );
+    let certChain = getCertChainAsString(message.failedCertChain);
+    ok(message.text.includes(certChain), "Found certificate chain");
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkUnknownIssuerLearnMoreLink() {
+  info(
+    "Loading a cert error for self-signed pages and checking the correct link is shown"
+  );
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(UNKNOWN_ISSUER, useFrame);
+    let browser = tab.linkedBrowser;
+
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    let href = await SpecialPowers.spawn(bc, [], async function () {
+      let learnMoreLink = content.document.getElementById("learnMoreLink");
+      return learnMoreLink.href;
+    });
+    ok(href.endsWith("security-error"), "security-error in the Learn More URL");
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkViewCertificate() {
+  info("Loading a cert error and checking that the certificate can be shown.");
+  for (let useFrame of [true, false]) {
+    if (useFrame) {
+      // Bug #1573502
+      continue;
+    }
+    let tab = await openErrorPage(UNKNOWN_ISSUER, useFrame);
+    let browser = tab.linkedBrowser;
+
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    let loaded = BrowserTestUtils.waitForNewTab(gBrowser, null, true);
+    await SpecialPowers.spawn(bc, [], async function () {
+      let viewCertificate = content.document.getElementById("viewCertificate");
+      viewCertificate.click();
+    });
+    await loaded;
+
+    let spec = gBrowser.selectedTab.linkedBrowser.documentURI.spec;
+    Assert.ok(
+      spec.startsWith("about:certificate"),
+      "about:certificate is the new opened tab"
+    );
+
+    await SpecialPowers.spawn(
+      gBrowser.selectedTab.linkedBrowser,
+      [],
+      async function () {
+        let doc = content.document;
+        let certificateSection = await ContentTaskUtils.waitForCondition(() => {
+          return doc.querySelector("certificate-section");
+        }, "Certificate section found");
+
+        let infoGroup =
+          certificateSection.shadowRoot.querySelector("info-group");
+        Assert.ok(infoGroup, "infoGroup found");
+
+        let items = infoGroup.shadowRoot.querySelectorAll("info-item");
+        let commonnameID = items[items.length - 1].shadowRoot
+          .querySelector("label")
+          .getAttribute("data-l10n-id");
+        Assert.equal(
+          commonnameID,
+          "certificate-viewer-common-name",
+          "The correct item was selected"
+        );
+
+        let commonnameValue =
+          items[items.length - 1].shadowRoot.querySelector(".info").textContent;
+        Assert.equal(
+          commonnameValue,
+          "self-signed.example.com",
+          "Shows the correct certificate in the page"
+        );
+      }
+    );
+    BrowserTestUtils.removeTab(gBrowser.selectedTab); // closes about:certificate
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkBadStsCertHeadline() {
+  info(
+    "Loading a bad sts cert error page and checking that the correct headline is shown"
+  );
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    let bc = browser.browsingContext;
+    if (useFrame) {
+      bc = bc.children[0];
+    }
+
+    await SpecialPowers.spawn(bc, [useFrame], async _useFrame => {
+      const titleText = content.document.querySelector(".title-text");
+      is(
+        titleText.dataset.l10nId,
+        _useFrame ? "nssBadCert-sts-title" : "nssBadCert-title",
+        "Error page title is set"
+      );
+    });
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkSandboxedIframe() {
+  info(
+    "Loading a bad sts cert error in a sandboxed iframe and check that the correct headline is shown"
+  );
+  let useFrame = true;
+  let sandboxed = true;
+  let tab = await openErrorPage(BAD_CERT, useFrame, sandboxed);
+  let browser = tab.linkedBrowser;
+
+  let bc = browser.browsingContext.children[0];
+  await SpecialPowers.spawn(bc, [], async function () {
+    let doc = content.document;
+
+    const titleText = doc.querySelector(".title-text");
+    is(
+      titleText.dataset.l10nId,
+      "nssBadCert-sts-title",
+      "Title shows Did Not Connect: Potential Security Issue"
+    );
+
+    const errorLabel = doc.querySelector(
+      '[data-l10n-id="cert-error-code-prefix-link"]'
+    );
+    const elArgs = JSON.parse(errorLabel.dataset.l10nArgs);
+    is(
+      elArgs.error,
+      "SEC_ERROR_EXPIRED_CERTIFICATE",
+      "Correct error message found"
+    );
+    is(
+      doc.getElementById("errorCode").tagName,
+      "a",
+      "Error message contains a link"
+    );
+  });
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+add_task(async function checkViewSource() {
+  info(
+    "Loading a bad sts cert error in a sandboxed iframe and check that the correct headline is shown"
+  );
+  let uri = "view-source:" + BAD_CERT;
+  let tab = await openErrorPage(uri);
+  let browser = tab.linkedBrowser;
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document;
+
+    const errorLabel = doc.querySelector(
+      '[data-l10n-id="cert-error-code-prefix-link"]'
+    );
+    const elArgs = JSON.parse(errorLabel.dataset.l10nArgs);
+    is(
+      elArgs.error,
+      "SEC_ERROR_EXPIRED_CERTIFICATE",
+      "Correct error message found"
+    );
+    is(
+      doc.getElementById("errorCode").tagName,
+      "a",
+      "Error message contains a link"
+    );
+
+    const titleText = doc.querySelector(".title-text");
+    is(titleText.dataset.l10nId, "nssBadCert-title", "Error page title is set");
+
+    const shortDesc = doc.getElementById("errorShortDesc");
+    const sdArgs = JSON.parse(shortDesc.dataset.l10nArgs);
+    is(
+      sdArgs.hostname,
+      "expired.example.com",
+      "Should list hostname in error message."
+    );
+  });
+
+  let loaded = BrowserTestUtils.browserLoaded(browser, false, uri);
+  info("Clicking the exceptionDialogButton in advanced panel");
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document;
+    let exceptionButton = doc.getElementById("exceptionDialogButton");
+    exceptionButton.click();
+  });
+
+  info("Loading the url after adding exception");
+  await loaded;
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document;
+    ok(
+      !doc.documentURI.startsWith("about:certerror"),
+      "Exception has been added"
+    );
+  });
+
+  let certOverrideService = Cc[
+    "@mozilla.org/security/certoverride;1"
+  ].getService(Ci.nsICertOverrideService);
+  certOverrideService.clearValidityOverride("expired.example.com", -1, {});
+
+  loaded = BrowserTestUtils.waitForErrorPage(browser);
+  BrowserReloadSkipCache();
+  await loaded;
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_clockSkew.js b/browser/base/content/test/about/browser_aboutCertError_clockSkew.js
new file mode 100644
index 0000000000..e3b77bd636
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_clockSkew.js
@@ -0,0 +1,153 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const PREF_SERVICES_SETTINGS_CLOCK_SKEW_SECONDS =
+  "services.settings.clock_skew_seconds";
+const PREF_SERVICES_SETTINGS_LAST_FETCHED =
+  "services.settings.last_update_seconds";
+
+add_task(async function checkWrongSystemTimeWarning() {
+  async function setUpPage() {
+    let browser;
+    let certErrorLoaded;
+    await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      () => {
+        gBrowser.selectedTab = BrowserTestUtils.addTab(
+          gBrowser,
+          "https://expired.example.com/"
+        );
+        browser = gBrowser.selectedBrowser;
+        certErrorLoaded = BrowserTestUtils.waitForErrorPage(browser);
+      },
+      false
+    );
+
+    info("Loading and waiting for the cert error");
+    await certErrorLoaded;
+
+    return SpecialPowers.spawn(browser, [], async function () {
+      let doc = content.document;
+      let div = doc.getElementById("errorShortDesc");
+      let learnMoreLink = doc.getElementById("learnMoreLink");
+
+      await ContentTaskUtils.waitForCondition(
+        () => div.textContent.includes("update your computer clock"),
+        "Correct error message found"
+      );
+
+      return {
+        divDisplay: content.getComputedStyle(div).display,
+        text: div.textContent,
+        learnMoreLink: learnMoreLink.href,
+      };
+    });
+  }
+
+  // Pretend that we recently updated our kinto clock skew pref
+  Services.prefs.setIntPref(
+    PREF_SERVICES_SETTINGS_LAST_FETCHED,
+    Math.floor(Date.now() / 1000)
+  );
+
+  // For this test, we want to trick Firefox into believing that
+  // the local system time (as returned by Date.now()) is wrong.
+  // Because we don't want to actually change the local system time,
+  // we will do the following:
+
+  // Take the validity date of our test page (expired.example.com).
+  let expiredDate = new Date("2010/01/05 12:00");
+  let localDate = Date.now();
+
+  // Compute the difference between the server date and the correct
+  // local system date.
+  let skew = Math.floor((localDate - expiredDate) / 1000);
+
+  // Make it seem like our reference server agrees that the certificate
+  // date is correct by recording the difference as clock skew.
+  Services.prefs.setIntPref(PREF_SERVICES_SETTINGS_CLOCK_SKEW_SECONDS, skew);
+
+  let localDateFmt = new Intl.DateTimeFormat("en-US", {
+    dateStyle: "medium",
+  }).format(localDate);
+
+  info("Loading a bad cert page with a skewed clock");
+  let message = await setUpPage();
+
+  isnot(
+    message.divDisplay,
+    "none",
+    "Wrong time message information is visible"
+  );
+  ok(
+    message.text.includes("update your computer clock"),
+    "Correct error message found"
+  );
+  ok(
+    message.text.includes("expired.example.com"),
+    "URL found in error message"
+  );
+  ok(message.text.includes(localDateFmt), "Correct local date displayed");
+  ok(
+    message.learnMoreLink.includes("time-errors"),
+    "time-errors in the Learn More URL"
+  );
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+
+  Services.prefs.clearUserPref(PREF_SERVICES_SETTINGS_LAST_FETCHED);
+  Services.prefs.clearUserPref(PREF_SERVICES_SETTINGS_CLOCK_SKEW_SECONDS);
+});
+
+add_task(async function checkCertError() {
+  async function setUpPage() {
+    let browser;
+    let certErrorLoaded;
+    gBrowser.selectedTab = BrowserTestUtils.addTab(
+      gBrowser,
+      "https://expired.example.com/"
+    );
+    browser = gBrowser.selectedBrowser;
+    certErrorLoaded = BrowserTestUtils.waitForErrorPage(browser);
+
+    info("Loading and waiting for the cert error");
+    await certErrorLoaded;
+
+    return SpecialPowers.spawn(browser, [], async function () {
+      let doc = content.document;
+      let el = doc.getElementById("errorWhatToDoText");
+      await ContentTaskUtils.waitForCondition(() => el.textContent);
+      return el.textContent;
+    });
+  }
+
+  // The particular error message will be displayed only when clock_skew_seconds is
+  // less or equal to a day and the difference between date.now() and last_fetched is less than
+  // or equal to 5 days. Setting the prefs accordingly.
+
+  Services.prefs.setIntPref(
+    PREF_SERVICES_SETTINGS_LAST_FETCHED,
+    Math.floor(Date.now() / 1000)
+  );
+
+  let skew = 60 * 60 * 24;
+  Services.prefs.setIntPref(PREF_SERVICES_SETTINGS_CLOCK_SKEW_SECONDS, skew);
+
+  info("Loading a bad cert page");
+  let message = await setUpPage();
+
+  ok(
+    message.includes(
+      "The issue is most likely with the website, and there is nothing you can do" +
+        " to resolve it. You can notify the website’s administrator about the problem."
+    ),
+    "Correct error message found"
+  );
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+
+  Services.prefs.clearUserPref(PREF_SERVICES_SETTINGS_LAST_FETCHED);
+  Services.prefs.clearUserPref(PREF_SERVICES_SETTINGS_CLOCK_SKEW_SECONDS);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_exception.js b/browser/base/content/test/about/browser_aboutCertError_exception.js
new file mode 100644
index 0000000000..7ee1bdde45
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_exception.js
@@ -0,0 +1,221 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const BAD_CERT = "https://expired.example.com/";
+const BAD_STS_CERT =
+  "https://badchain.include-subdomains.pinning.example.com:443";
+const PREF_PERMANENT_OVERRIDE = "security.certerrors.permanentOverride";
+
+add_task(async function checkExceptionDialogButton() {
+  info(
+    "Loading a bad cert page and making sure the exceptionDialogButton directly adds an exception"
+  );
+  let tab = await openErrorPage(BAD_CERT);
+  let browser = tab.linkedBrowser;
+  let loaded = BrowserTestUtils.browserLoaded(browser, false, BAD_CERT);
+  info("Clicking the exceptionDialogButton in advanced panel");
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document;
+    let exceptionButton = doc.getElementById("exceptionDialogButton");
+    exceptionButton.click();
+  });
+
+  info("Loading the url after adding exception");
+  await loaded;
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document;
+    ok(
+      !doc.documentURI.startsWith("about:certerror"),
+      "Exception has been added"
+    );
+  });
+
+  let certOverrideService = Cc[
+    "@mozilla.org/security/certoverride;1"
+  ].getService(Ci.nsICertOverrideService);
+  certOverrideService.clearValidityOverride("expired.example.com", -1, {});
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+add_task(async function checkPermanentExceptionPref() {
+  info(
+    "Loading a bad cert page and making sure the permanent state of exceptions can be controlled via pref"
+  );
+
+  for (let permanentOverride of [false, true]) {
+    Services.prefs.setBoolPref(PREF_PERMANENT_OVERRIDE, permanentOverride);
+
+    let tab = await openErrorPage(BAD_CERT);
+    let browser = tab.linkedBrowser;
+    let loaded = BrowserTestUtils.browserLoaded(browser, false, BAD_CERT);
+    info("Clicking the exceptionDialogButton in advanced panel");
+    let serverCertBytes = await SpecialPowers.spawn(
+      browser,
+      [],
+      async function () {
+        let doc = content.document;
+        let exceptionButton = doc.getElementById("exceptionDialogButton");
+        exceptionButton.click();
+        return content.docShell.failedChannel.securityInfo.serverCert.getRawDER();
+      }
+    );
+
+    info("Loading the url after adding exception");
+    await loaded;
+
+    await SpecialPowers.spawn(browser, [], async function () {
+      let doc = content.document;
+      ok(
+        !doc.documentURI.startsWith("about:certerror"),
+        "Exception has been added"
+      );
+    });
+
+    let certOverrideService = Cc[
+      "@mozilla.org/security/certoverride;1"
+    ].getService(Ci.nsICertOverrideService);
+
+    let isTemporary = {};
+    let certdb = Cc["@mozilla.org/security/x509certdb;1"].getService(
+      Ci.nsIX509CertDB
+    );
+    let cert = certdb.constructX509(serverCertBytes);
+    let hasException = certOverrideService.hasMatchingOverride(
+      "expired.example.com",
+      -1,
+      {},
+      cert,
+      isTemporary
+    );
+    ok(hasException, "Has stored an exception for the page.");
+    is(
+      isTemporary.value,
+      !permanentOverride,
+      `Has stored a ${
+        permanentOverride ? "permanent" : "temporary"
+      } exception for the page.`
+    );
+
+    certOverrideService.clearValidityOverride("expired.example.com", -1, {});
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+
+  Services.prefs.clearUserPref(PREF_PERMANENT_OVERRIDE);
+});
+
+add_task(async function checkBadStsCert() {
+  info("Loading a badStsCert and making sure exception button doesn't show up");
+
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_STS_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    await SpecialPowers.spawn(
+      browser,
+      [{ frame: useFrame }],
+      async function ({ frame }) {
+        let doc = frame
+          ? content.document.querySelector("iframe").contentDocument
+          : content.document;
+        let exceptionButton = doc.getElementById("exceptionDialogButton");
+        ok(
+          ContentTaskUtils.is_hidden(exceptionButton),
+          "Exception button is hidden."
+        );
+      }
+    );
+
+    let message = await SpecialPowers.spawn(
+      browser,
+      [{ frame: useFrame }],
+      async function ({ frame }) {
+        let doc = frame
+          ? content.document.querySelector("iframe").contentDocument
+          : content.document;
+        let advancedButton = doc.getElementById("advancedButton");
+        advancedButton.click();
+
+        // aboutNetError.mjs is using async localization to format several
+        // messages and in result the translation may be applied later.
+        // We want to return the textContent of the element only after
+        // the translation completes, so let's wait for it here.
+        let elements = [doc.getElementById("badCertTechnicalInfo")];
+        await ContentTaskUtils.waitForCondition(() => {
+          return elements.every(elem => !!elem.textContent.trim().length);
+        });
+
+        return doc.getElementById("badCertTechnicalInfo").textContent;
+      }
+    );
+    ok(
+      message.includes("SSL_ERROR_BAD_CERT_DOMAIN"),
+      "Didn't find SSL_ERROR_BAD_CERT_DOMAIN."
+    );
+    ok(
+      message.includes("The certificate is only valid for"),
+      "Didn't find error message."
+    );
+    ok(
+      message.includes("a certificate that is not valid for"),
+      "Didn't find error message."
+    );
+    ok(
+      message.includes("badchain.include-subdomains.pinning.example.com"),
+      "Didn't find domain in error message."
+    );
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+});
+
+add_task(async function checkhideAddExceptionButtonViaPref() {
+  info(
+    "Loading a bad cert page and verifying the pref security.certerror.hideAddException"
+  );
+  Services.prefs.setBoolPref("security.certerror.hideAddException", true);
+
+  for (let useFrame of [false, true]) {
+    let tab = await openErrorPage(BAD_CERT, useFrame);
+    let browser = tab.linkedBrowser;
+
+    await SpecialPowers.spawn(
+      browser,
+      [{ frame: useFrame }],
+      async function ({ frame }) {
+        let doc = frame
+          ? content.document.querySelector("iframe").contentDocument
+          : content.document;
+
+        let exceptionButton = doc.getElementById("exceptionDialogButton");
+        ok(
+          ContentTaskUtils.is_hidden(exceptionButton),
+          "Exception button is hidden."
+        );
+      }
+    );
+
+    BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  }
+
+  Services.prefs.clearUserPref("security.certerror.hideAddException");
+});
+
+add_task(async function checkhideAddExceptionButtonInFrames() {
+  info("Loading a bad cert page in a frame and verifying it's hidden.");
+  let tab = await openErrorPage(BAD_CERT, true);
+  let browser = tab.linkedBrowser;
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let doc = content.document.querySelector("iframe").contentDocument;
+    let exceptionButton = doc.getElementById("exceptionDialogButton");
+    ok(
+      ContentTaskUtils.is_hidden(exceptionButton),
+      "Exception button is hidden."
+    );
+  });
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_mitm.js b/browser/base/content/test/about/browser_aboutCertError_mitm.js
new file mode 100644
index 0000000000..5c9b5e8144
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_mitm.js
@@ -0,0 +1,158 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const PREF_MITM_PRIMING = "security.certerrors.mitm.priming.enabled";
+const PREF_MITM_PRIMING_ENDPOINT = "security.certerrors.mitm.priming.endpoint";
+const PREF_MITM_CANARY_ISSUER = "security.pki.mitm_canary_issuer";
+const PREF_MITM_AUTO_ENABLE_ENTERPRISE_ROOTS =
+  "security.certerrors.mitm.auto_enable_enterprise_roots";
+const PREF_ENTERPRISE_ROOTS = "security.enterprise_roots.enabled";
+
+const UNKNOWN_ISSUER = "https://untrusted.example.com";
+
+// Check that basic MitM priming works and the MitM error page is displayed successfully.
+add_task(async function checkMitmPriming() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [PREF_MITM_PRIMING, true],
+      [PREF_MITM_PRIMING_ENDPOINT, UNKNOWN_ISSUER],
+    ],
+  });
+
+  let browser;
+  let certErrorLoaded;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, UNKNOWN_ISSUER);
+      browser = gBrowser.selectedBrowser;
+      // The page will reload by itself after the initial canary request, so we wait
+      // until the AboutNetErrorLoad event has happened twice.
+      certErrorLoaded = new Promise(resolve => {
+        let loaded = 0;
+        let removeEventListener = BrowserTestUtils.addContentEventListener(
+          browser,
+          "AboutNetErrorLoad",
+          () => {
+            if (++loaded == 2) {
+              removeEventListener();
+              resolve();
+            }
+          },
+          { capture: false, wantUntrusted: true }
+        );
+      });
+    },
+    false
+  );
+
+  await certErrorLoaded;
+
+  await SpecialPowers.spawn(browser, [], () => {
+    is(
+      content.document.body.getAttribute("code"),
+      "MOZILLA_PKIX_ERROR_MITM_DETECTED",
+      "MitM error page has loaded."
+    );
+  });
+
+  ok(true, "Successfully loaded the MitM error page.");
+
+  is(
+    Services.prefs.getStringPref(PREF_MITM_CANARY_ISSUER),
+    "CN=Unknown CA",
+    "Stored the correct issuer"
+  );
+
+  await SpecialPowers.spawn(browser, [], async () => {
+    const shortDesc = content.document.querySelector("#errorShortDesc");
+    const whatToDo = content.document.querySelector("#errorWhatToDoText");
+
+    await ContentTaskUtils.waitForCondition(
+      () => shortDesc.textContent != "" && whatToDo.textContent != "",
+      "DOM localization has been updated"
+    );
+
+    ok(
+      shortDesc.textContent.includes("Unknown CA"),
+      "Shows the name of the issuer."
+    );
+
+    ok(
+      whatToDo.textContent.includes("Unknown CA"),
+      "Shows the name of the issuer."
+    );
+  });
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+
+  Services.prefs.clearUserPref(PREF_MITM_CANARY_ISSUER);
+});
+
+// Check that we set the enterprise roots pref correctly on MitM
+add_task(async function checkMitmAutoEnableEnterpriseRoots() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [PREF_MITM_PRIMING, true],
+      [PREF_MITM_PRIMING_ENDPOINT, UNKNOWN_ISSUER],
+      [PREF_MITM_AUTO_ENABLE_ENTERPRISE_ROOTS, true],
+      [PREF_ENTERPRISE_ROOTS, false],
+    ],
+  });
+
+  let browser;
+  let certErrorLoaded;
+
+  let prefChanged = TestUtils.waitForPrefChange(
+    PREF_ENTERPRISE_ROOTS,
+    value => value === true
+  );
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, UNKNOWN_ISSUER);
+      browser = gBrowser.selectedBrowser;
+      // The page will reload by itself after the initial canary request, so we wait
+      // until the AboutNetErrorLoad event has happened twice.
+      certErrorLoaded = new Promise(resolve => {
+        let loaded = 0;
+        let removeEventListener = BrowserTestUtils.addContentEventListener(
+          browser,
+          "AboutNetErrorLoad",
+          () => {
+            if (++loaded == 2) {
+              removeEventListener();
+              resolve();
+            }
+          },
+          { capture: false, wantUntrusted: true }
+        );
+      });
+    },
+    false
+  );
+
+  await certErrorLoaded;
+  await prefChanged;
+
+  await SpecialPowers.spawn(browser, [], () => {
+    is(
+      content.document.body.getAttribute("code"),
+      "MOZILLA_PKIX_ERROR_MITM_DETECTED",
+      "MitM error page has loaded."
+    );
+  });
+
+  ok(true, "Successfully loaded the MitM error page.");
+
+  ok(
+    !Services.prefs.prefHasUserValue(PREF_ENTERPRISE_ROOTS),
+    "Flipped the enterprise roots pref back"
+  );
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+
+  Services.prefs.clearUserPref(PREF_MITM_CANARY_ISSUER);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_noSubjectAltName.js b/browser/base/content/test/about/browser_aboutCertError_noSubjectAltName.js
new file mode 100644
index 0000000000..1a2add1c96
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_noSubjectAltName.js
@@ -0,0 +1,67 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const BROWSER_NAME = document
+  .getElementById("bundle_brand")
+  .getString("brandShortName");
+const UNKNOWN_ISSUER = "https://no-subject-alt-name.example.com:443";
+
+const checkAdvancedAndGetTechnicalInfoText = async () => {
+  let doc = content.document;
+
+  let advancedButton = doc.getElementById("advancedButton");
+  ok(advancedButton, "advancedButton found");
+  is(
+    advancedButton.hasAttribute("disabled"),
+    false,
+    "advancedButton should be clickable"
+  );
+  advancedButton.click();
+
+  let badCertAdvancedPanel = doc.getElementById("badCertAdvancedPanel");
+  ok(badCertAdvancedPanel, "badCertAdvancedPanel found");
+
+  let badCertTechnicalInfo = doc.getElementById("badCertTechnicalInfo");
+  ok(badCertTechnicalInfo, "badCertTechnicalInfo found");
+
+  // Wait until fluent sets the errorCode inner text.
+  await ContentTaskUtils.waitForCondition(() => {
+    let errorCode = doc.getElementById("errorCode");
+    return errorCode.textContent == "SSL_ERROR_BAD_CERT_DOMAIN";
+  }, "correct error code has been set inside the advanced button panel");
+
+  let viewCertificate = doc.getElementById("viewCertificate");
+  ok(viewCertificate, "viewCertificate found");
+
+  return badCertTechnicalInfo.innerHTML;
+};
+
+const checkCorrectMessages = message => {
+  let isCorrectMessage = message.includes(
+    "Websites prove their identity via certificates. " +
+      BROWSER_NAME +
+      " does not trust this site because it uses a certificate that is" +
+      " not valid for no-subject-alt-name.example.com"
+  );
+  is(isCorrectMessage, true, "That message should appear");
+  let isWrongMessage = message.includes("The certificate is only valid for ");
+  is(isWrongMessage, false, "That message shouldn't appear");
+};
+
+add_task(async function checkUntrustedCertError() {
+  info(
+    `Loading ${UNKNOWN_ISSUER} which does not have a subject specified in the certificate`
+  );
+  let tab = await openErrorPage(UNKNOWN_ISSUER);
+  let browser = tab.linkedBrowser;
+  info("Clicking the exceptionDialogButton in advanced panel");
+  let badCertTechnicalInfoText = await SpecialPowers.spawn(
+    browser,
+    [],
+    checkAdvancedAndGetTechnicalInfoText
+  );
+  checkCorrectMessages(badCertTechnicalInfoText, browser);
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_offlineSupport.js b/browser/base/content/test/about/browser_aboutCertError_offlineSupport.js
new file mode 100644
index 0000000000..5b717a683a
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_offlineSupport.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const BAD_CERT_PAGE = "https://expired.example.com";
+const DUMMY_SUPPORT_BASE_PATH = "/1/firefox/fxVersion/OSVersion/language/";
+const DUMMY_SUPPORT_URL = BAD_CERT_PAGE + DUMMY_SUPPORT_BASE_PATH;
+const OFFLINE_SUPPORT_PAGE =
+  "chrome://global/content/neterror/supportpages/time-errors.html";
+
+add_task(async function testOfflineSupportPage() {
+  // Cache the original value of app.support.baseURL pref to reset later
+  let originalBaseURL = Services.prefs.getCharPref("app.support.baseURL");
+
+  Services.prefs.setCharPref("app.support.baseURL", DUMMY_SUPPORT_URL);
+  let errorTab = await openErrorPage(BAD_CERT_PAGE);
+
+  let offlineSupportPromise = BrowserTestUtils.waitForNewTab(
+    gBrowser,
+    DUMMY_SUPPORT_URL + "time-errors"
+  );
+  await SpecialPowers.spawn(
+    errorTab.linkedBrowser,
+    [DUMMY_SUPPORT_URL],
+    async expectedURL => {
+      let doc = content.document;
+
+      let learnMoreLink = doc.getElementById("learnMoreLink");
+      let supportPageURL = learnMoreLink.getAttribute("href");
+      ok(
+        supportPageURL == expectedURL + "time-errors",
+        "Correct support page URL has been set"
+      );
+      await EventUtils.synthesizeMouseAtCenter(learnMoreLink, {}, content);
+    }
+  );
+  let offlineSupportTab = await offlineSupportPromise;
+  await BrowserTestUtils.browserLoaded(
+    gBrowser.selectedBrowser,
+    false,
+    OFFLINE_SUPPORT_PAGE
+  );
+
+  // Reset this pref instead of clearing it to maintain globally set
+  // custom value for testing purposes.
+  Services.prefs.setCharPref("app.support.baseURL", originalBaseURL);
+
+  await BrowserTestUtils.removeTab(offlineSupportTab);
+  await BrowserTestUtils.removeTab(errorTab);
+});
diff --git a/browser/base/content/test/about/browser_aboutCertError_telemetry.js b/browser/base/content/test/about/browser_aboutCertError_telemetry.js
new file mode 100644
index 0000000000..61ec8afcbf
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutCertError_telemetry.js
@@ -0,0 +1,164 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+requestLongerTimeout(2);
+
+const BAD_CERT = "https://expired.example.com/";
+const BAD_STS_CERT =
+  "https://badchain.include-subdomains.pinning.example.com:443";
+
+add_task(async function checkTelemetryClickEvents() {
+  info("Loading a bad cert page and verifying telemetry click events arrive.");
+
+  let oldCanRecord = Services.telemetry.canRecordExtended;
+  Services.telemetry.canRecordExtended = true;
+
+  registerCleanupFunction(() => {
+    Services.telemetry.canRecordExtended = oldCanRecord;
+  });
+
+  // For obvious reasons event telemetry in the content processes updates with
+  // the main processs asynchronously, so we need to wait for the main process
+  // to catch up through the entire test.
+
+  // There's an arbitrary interval of 2 seconds in which the content
+  // processes sync their event data with the parent process, we wait
+  // this out to ensure that we clear everything that is left over from
+  // previous tests and don't receive random events in the middle of our tests.
+  // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+  await new Promise(c => setTimeout(c, 2000));
+
+  // Clear everything.
+  Services.telemetry.clearEvents();
+  await TestUtils.waitForCondition(() => {
+    let events = Services.telemetry.snapshotEvents(
+      Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+      true
+    ).content;
+    return !events || !events.length;
+  });
+
+  // Now enable recording our telemetry. Even if this is disabled, content
+  // processes will send event telemetry to the parent, thus we needed to ensure
+  // we waited and cleared first. Sigh.
+  Services.telemetry.setEventRecordingEnabled("security.ui.certerror", true);
+
+  for (let useFrame of [false, true]) {
+    let recordedObjects = [
+      "advanced_button",
+      "learn_more_link",
+      "error_code_link",
+      "clipboard_button_top",
+      "clipboard_button_bot",
+      "return_button_top",
+    ];
+
+    recordedObjects.push("return_button_adv");
+    if (!useFrame) {
+      recordedObjects.push("exception_button");
+    }
+
+    for (let object of recordedObjects) {
+      let tab = await openErrorPage(BAD_CERT, useFrame);
+      let browser = tab.linkedBrowser;
+
+      let loadEvents = await TestUtils.waitForCondition(() => {
+        let events = Services.telemetry.snapshotEvents(
+          Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+          true
+        ).content;
+        if (events && events.length) {
+          events = events.filter(
+            e => e[1] == "security.ui.certerror" && e[2] == "load"
+          );
+          if (
+            events.length == 1 &&
+            events[0][5].is_frame == useFrame.toString()
+          ) {
+            return events;
+          }
+        }
+        return null;
+      }, "recorded telemetry for the load");
+
+      is(
+        loadEvents.length,
+        1,
+        `recorded telemetry for the load testing ${object}, useFrame: ${useFrame}`
+      );
+
+      let bc = browser.browsingContext;
+      if (useFrame) {
+        bc = bc.children[0];
+      }
+
+      await SpecialPowers.spawn(bc, [object], async function (objectId) {
+        let doc = content.document;
+
+        await ContentTaskUtils.waitForCondition(
+          () => doc.body.classList.contains("certerror"),
+          "Wait for certerror to be loaded"
+        );
+
+        let domElement = doc.querySelector(`[data-telemetry-id='${objectId}']`);
+        domElement.click();
+      });
+
+      let clickEvents = await TestUtils.waitForCondition(() => {
+        let events = Services.telemetry.snapshotEvents(
+          Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+          true
+        ).content;
+        if (events && events.length) {
+          events = events.filter(
+            e =>
+              e[1] == "security.ui.certerror" &&
+              e[2] == "click" &&
+              e[3] == object
+          );
+          if (
+            events.length == 1 &&
+            events[0][5].is_frame == useFrame.toString()
+          ) {
+            return events;
+          }
+        }
+        return null;
+      }, "Has captured telemetry events.");
+
+      is(
+        clickEvents.length,
+        1,
+        `recorded telemetry for the click on ${object}, useFrame: ${useFrame}`
+      );
+
+      // We opened an extra tab for the SUMO page, need to close it.
+      if (object == "learn_more_link") {
+        BrowserTestUtils.removeTab(gBrowser.selectedTab);
+      }
+
+      if (object == "exception_button") {
+        let certOverrideService = Cc[
+          "@mozilla.org/security/certoverride;1"
+        ].getService(Ci.nsICertOverrideService);
+        certOverrideService.clearValidityOverride(
+          "expired.example.com",
+          -1,
+          {}
+        );
+      }
+
+      BrowserTestUtils.removeTab(gBrowser.selectedTab);
+    }
+  }
+
+  let enableCertErrorUITelemetry = Services.prefs.getBoolPref(
+    "security.certerrors.recordEventTelemetry"
+  );
+  Services.telemetry.setEventRecordingEnabled(
+    "security.ui.certerror",
+    enableCertErrorUITelemetry
+  );
+});
diff --git a/browser/base/content/test/about/browser_aboutDialog_distribution.js b/browser/base/content/test/about/browser_aboutDialog_distribution.js
new file mode 100644
index 0000000000..8f52533bbc
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutDialog_distribution.js
@@ -0,0 +1,66 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/toolkit/mozapps/update/tests/browser/head.js",
+  this
+);
+
+add_task(async function verify_distribution_info_hides() {
+  let defaultBranch = Services.prefs.getDefaultBranch(null);
+
+  defaultBranch.setCharPref("distribution.id", "mozilla-test-distribution-id");
+  defaultBranch.setCharPref("distribution.version", "1.0");
+
+  let aboutDialog = await waitForAboutDialog();
+
+  let distroIdField = aboutDialog.document.getElementById("distributionId");
+  let distroField = aboutDialog.document.getElementById("distribution");
+
+  if (
+    AppConstants.platform === "win" &&
+    Services.sysinfo.getProperty("hasWinPackageId")
+  ) {
+    is(distroIdField.value, "mozilla-test-distribution-id - 1.0");
+    is(distroIdField.style.display, "block");
+    is(distroField.style.display, "block");
+  } else {
+    is(distroIdField.value, "");
+    isnot(distroIdField.style.display, "block");
+    isnot(distroField.style.display, "block");
+  }
+
+  aboutDialog.close();
+});
+
+add_task(async function verify_distribution_info_displays() {
+  let defaultBranch = Services.prefs.getDefaultBranch(null);
+
+  defaultBranch.setCharPref("distribution.id", "test-distribution-id");
+  defaultBranch.setCharPref("distribution.version", "1.0");
+  defaultBranch.setCharPref("distribution.about", "About Text");
+
+  let aboutDialog = await waitForAboutDialog();
+
+  let distroIdField = aboutDialog.document.getElementById("distributionId");
+
+  is(distroIdField.value, "test-distribution-id - 1.0");
+  is(distroIdField.style.display, "block");
+
+  let distroField = aboutDialog.document.getElementById("distribution");
+  is(distroField.value, "About Text");
+  is(distroField.style.display, "block");
+
+  aboutDialog.close();
+});
+
+add_task(async function cleanup() {
+  let defaultBranch = Services.prefs.getDefaultBranch(null);
+
+  // This is the best we can do since we can't remove default prefs
+  defaultBranch.setCharPref("distribution.id", "");
+  defaultBranch.setCharPref("distribution.version", "");
+  defaultBranch.setCharPref("distribution.about", "");
+});
diff --git a/browser/base/content/test/about/browser_aboutHome_search_POST.js b/browser/base/content/test/about/browser_aboutHome_search_POST.js
new file mode 100644
index 0000000000..c892198207
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutHome_search_POST.js
@@ -0,0 +1,104 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+ignoreAllUncaughtExceptions();
+
+add_task(async function () {
+  info("Check POST search engine support");
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [
+        "browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar",
+        false,
+      ],
+    ],
+  });
+
+  let currEngine = await Services.search.getDefault();
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:home" },
+    async browser => {
+      let observerPromise = new Promise(resolve => {
+        let searchObserver = async function search_observer(
+          subject,
+          topic,
+          data
+        ) {
+          let engine = subject.QueryInterface(Ci.nsISearchEngine);
+          info("Observer: " + data + " for " + engine.name);
+
+          if (data != "engine-added") {
+            return;
+          }
+
+          if (engine.name != "POST Search") {
+            return;
+          }
+
+          Services.obs.removeObserver(
+            searchObserver,
+            "browser-search-engine-modified"
+          );
+
+          resolve(engine);
+        };
+
+        Services.obs.addObserver(
+          searchObserver,
+          "browser-search-engine-modified"
+        );
+      });
+
+      let engine;
+      await promiseContentSearchChange(browser, async () => {
+        Services.search.addOpenSearchEngine(
+          // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+          "http://test:80/browser/browser/base/content/test/about/POSTSearchEngine.xml",
+          null
+        );
+
+        engine = await observerPromise;
+        Services.search.setDefault(
+          engine,
+          Ci.nsISearchService.CHANGE_REASON_UNKNOWN
+        );
+        return engine.name;
+      });
+
+      // Ready to execute the tests!
+      let needle = "Search for something awesome.";
+
+      let promise = BrowserTestUtils.browserLoaded(browser);
+      await SpecialPowers.spawn(browser, [{ needle }], async function (args) {
+        let doc = content.document;
+        let el = doc.querySelector(["#searchText", "#newtab-search-text"]);
+        el.value = args.needle;
+        doc.getElementById("searchSubmit").click();
+      });
+
+      await promise;
+
+      // When the search results load, check them for correctness.
+      await SpecialPowers.spawn(browser, [{ needle }], async function (args) {
+        let loadedText = content.document.body.textContent;
+        ok(loadedText, "search page loaded");
+        is(
+          loadedText,
+          "searchterms=" + escape(args.needle.replace(/\s/g, "+")),
+          "Search text should arrive correctly"
+        );
+      });
+
+      await Services.search.setDefault(
+        currEngine,
+        Ci.nsISearchService.CHANGE_REASON_UNKNOWN
+      );
+      try {
+        await Services.search.removeEngine(engine);
+      } catch (ex) {}
+    }
+  );
+  await SpecialPowers.popPrefEnv();
+});
diff --git a/browser/base/content/test/about/browser_aboutHome_search_composing.js b/browser/base/content/test/about/browser_aboutHome_search_composing.js
new file mode 100644
index 0000000000..309f1f674a
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutHome_search_composing.js
@@ -0,0 +1,110 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+ignoreAllUncaughtExceptions();
+
+add_task(async function () {
+  info("Clicking suggestion list while composing");
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [
+        "browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar",
+        false,
+      ],
+    ],
+  });
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:home" },
+    async function (browser) {
+      // Add a test engine that provides suggestions and switch to it.
+      let engine;
+      await promiseContentSearchChange(browser, async () => {
+        engine = await SearchTestUtils.promiseNewSearchEngine({
+          url: getRootDirectory(gTestPath) + "searchSuggestionEngine.xml",
+          setAsDefault: true,
+        });
+        return engine.name;
+      });
+
+      // Clear any search history results
+      await FormHistory.update({ op: "remove" });
+
+      await SpecialPowers.spawn(browser, [], async function () {
+        // Start composition and type "x"
+        let input = content.document.querySelector([
+          "#searchText",
+          "#newtab-search-text",
+        ]);
+        input.focus();
+      });
+
+      info("Setting up the mutation observer before synthesizing composition");
+      let mutationPromise = SpecialPowers.spawn(browser, [], async function () {
+        let searchController = content.wrappedJSObject.gContentSearchController;
+
+        // Wait for the search suggestions to become visible.
+        let table = searchController._suggestionsList;
+        let input = content.document.querySelector([
+          "#searchText",
+          "#newtab-search-text",
+        ]);
+
+        await ContentTaskUtils.waitForMutationCondition(
+          input,
+          { attributeFilter: ["aria-expanded"] },
+          () => input.getAttribute("aria-expanded") == "true"
+        );
+        ok(!table.hidden, "Search suggestion table unhidden");
+
+        let row = table.children[1];
+        row.setAttribute("id", "TEMPID");
+
+        // ContentSearchUIController looks at the current selectedIndex when
+        // performing a search. Synthesizing the mouse event on the suggestion
+        // doesn't actually mouseover the suggestion and trigger it to be flagged
+        // as selected, so we manually select it first.
+        searchController.selectedIndex = 1;
+      });
+
+      // FYI: "compositionstart" will be dispatched automatically.
+      await BrowserTestUtils.synthesizeCompositionChange(
+        {
+          composition: {
+            string: "x",
+            clauses: [
+              { length: 1, attr: Ci.nsITextInputProcessor.ATTR_RAW_CLAUSE },
+            ],
+          },
+          caret: { start: 1, length: 0 },
+        },
+        browser
+      );
+
+      info("Waiting for search suggestion table unhidden");
+      await mutationPromise;
+
+      // Click the second suggestion.
+      let expectedURL = (await Services.search.getDefault()).getSubmission(
+        "xbar",
+        null,
+        "homepage"
+      ).uri.spec;
+      let loadPromise = BrowserTestUtils.waitForDocLoadAndStopIt(
+        expectedURL,
+        gBrowser.selectedBrowser
+      );
+      await BrowserTestUtils.synthesizeMouseAtCenter(
+        "#TEMPID",
+        {
+          button: 0,
+        },
+        browser
+      );
+      await loadPromise;
+    }
+  );
+  await SpecialPowers.popPrefEnv();
+});
diff --git a/browser/base/content/test/about/browser_aboutHome_search_searchbar.js b/browser/base/content/test/about/browser_aboutHome_search_searchbar.js
new file mode 100644
index 0000000000..7b08d2ae34
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutHome_search_searchbar.js
@@ -0,0 +1,44 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+const { CustomizableUITestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/CustomizableUITestUtils.sys.mjs"
+);
+let gCUITestUtils = new CustomizableUITestUtils(window);
+
+ignoreAllUncaughtExceptions();
+
+add_task(async function test_setup() {
+  await gCUITestUtils.addSearchBar();
+  registerCleanupFunction(() => {
+    gCUITestUtils.removeSearchBar();
+  });
+});
+
+add_task(async function () {
+  info("Cmd+k should focus the search box in the toolbar when it's present");
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:home" },
+    async function (browser) {
+      await BrowserTestUtils.synthesizeMouseAtCenter("#brandLogo", {}, browser);
+
+      let doc = window.document;
+      let searchInput = BrowserSearch.searchBar.textbox;
+      isnot(
+        searchInput,
+        doc.activeElement,
+        "Search bar should not be the active element."
+      );
+
+      EventUtils.synthesizeKey("k", { accelKey: true });
+      await TestUtils.waitForCondition(() => doc.activeElement === searchInput);
+      is(
+        searchInput,
+        doc.activeElement,
+        "Search bar should be the active element."
+      );
+    }
+  );
+});
diff --git a/browser/base/content/test/about/browser_aboutHome_search_suggestion.js b/browser/base/content/test/about/browser_aboutHome_search_suggestion.js
new file mode 100644
index 0000000000..4e1da9fe3e
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutHome_search_suggestion.js
@@ -0,0 +1,78 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+ignoreAllUncaughtExceptions();
+
+add_task(async function () {
+  // See browser_contentSearchUI.js for comprehensive content search UI tests.
+  info("Search suggestion smoke test");
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [
+        "browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar",
+        false,
+      ],
+    ],
+  });
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:home" },
+    async function (browser) {
+      // Add a test engine that provides suggestions and switch to it.
+      let engine;
+      await promiseContentSearchChange(browser, async () => {
+        engine = await SearchTestUtils.promiseNewSearchEngine({
+          url: getRootDirectory(gTestPath) + "searchSuggestionEngine.xml",
+          setAsDefault: true,
+        });
+        await Services.search.setDefault(
+          engine,
+          Ci.nsISearchService.CHANGE_REASON_UNKNOWN
+        );
+        return engine.name;
+      });
+
+      await SpecialPowers.spawn(browser, [], async function () {
+        // Type an X in the search input.
+        let input = content.document.querySelector([
+          "#searchText",
+          "#newtab-search-text",
+        ]);
+        input.focus();
+      });
+
+      await BrowserTestUtils.synthesizeKey("x", {}, browser);
+
+      await SpecialPowers.spawn(browser, [], async function () {
+        // Wait for the search suggestions to become visible.
+        let table = content.document.getElementById("searchSuggestionTable");
+        let input = content.document.querySelector([
+          "#searchText",
+          "#newtab-search-text",
+        ]);
+
+        await ContentTaskUtils.waitForMutationCondition(
+          input,
+          { attributeFilter: ["aria-expanded"] },
+          () => input.getAttribute("aria-expanded") == "true"
+        );
+        ok(!table.hidden, "Search suggestion table unhidden");
+      });
+
+      // Empty the search input, causing the suggestions to be hidden.
+      await BrowserTestUtils.synthesizeKey("a", { accelKey: true }, browser);
+      await BrowserTestUtils.synthesizeKey("VK_DELETE", {}, browser);
+
+      await SpecialPowers.spawn(browser, [], async function () {
+        let table = content.document.getElementById("searchSuggestionTable");
+        await ContentTaskUtils.waitForCondition(
+          () => table.hidden,
+          "Search suggestion table hidden"
+        );
+      });
+    }
+  );
+  await SpecialPowers.popPrefEnv();
+});
diff --git a/browser/base/content/test/about/browser_aboutHome_search_telemetry.js b/browser/base/content/test/about/browser_aboutHome_search_telemetry.js
new file mode 100644
index 0000000000..e23d07aa38
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutHome_search_telemetry.js
@@ -0,0 +1,101 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+ignoreAllUncaughtExceptions();
+
+add_task(async function () {
+  info(
+    "Check that performing a search fires a search event and records to Telemetry."
+  );
+
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [
+        "browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar",
+        false,
+      ],
+    ],
+  });
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:home" },
+    async function (browser) {
+      let engine;
+      await promiseContentSearchChange(browser, async () => {
+        engine = await SearchTestUtils.promiseNewSearchEngine({
+          url: getRootDirectory(gTestPath) + "searchSuggestionEngine.xml",
+          setAsDefault: true,
+        });
+        return engine.name;
+      });
+
+      await SpecialPowers.spawn(
+        browser,
+        [{ expectedName: engine.name }],
+        async function (args) {
+          let engineName =
+            content.wrappedJSObject.gContentSearchController.defaultEngine.name;
+          is(
+            engineName,
+            args.expectedName,
+            "Engine name in DOM should match engine we just added"
+          );
+        }
+      );
+
+      let numSearchesBefore = 0;
+      // Get the current number of recorded searches.
+      let histogramKey = `other-${engine.name}.abouthome`;
+      try {
+        let hs = Services.telemetry
+          .getKeyedHistogramById("SEARCH_COUNTS")
+          .snapshot();
+        if (histogramKey in hs) {
+          numSearchesBefore = hs[histogramKey].sum;
+        }
+      } catch (ex) {
+        // No searches performed yet, not a problem, |numSearchesBefore| is 0.
+      }
+
+      let searchStr = "a search";
+
+      let expectedURL = (await Services.search.getDefault()).getSubmission(
+        searchStr,
+        null,
+        "homepage"
+      ).uri.spec;
+      let promise = BrowserTestUtils.waitForDocLoadAndStopIt(
+        expectedURL,
+        browser
+      );
+
+      // Perform a search to increase the SEARCH_COUNT histogram.
+      await SpecialPowers.spawn(
+        browser,
+        [{ searchStr }],
+        async function (args) {
+          let doc = content.document;
+          info("Perform a search.");
+          let el = doc.querySelector(["#searchText", "#newtab-search-text"]);
+          el.value = args.searchStr;
+          doc.getElementById("searchSubmit").click();
+        }
+      );
+
+      await promise;
+
+      // Make sure the SEARCH_COUNTS histogram has the right key and count.
+      let hs = Services.telemetry
+        .getKeyedHistogramById("SEARCH_COUNTS")
+        .snapshot();
+      Assert.ok(histogramKey in hs, "histogram with key should be recorded");
+      Assert.equal(
+        hs[histogramKey].sum,
+        numSearchesBefore + 1,
+        "histogram sum should be incremented"
+      );
+    }
+  );
+  await SpecialPowers.popPrefEnv();
+});
diff --git a/browser/base/content/test/about/browser_aboutNetError.js b/browser/base/content/test/about/browser_aboutNetError.js
new file mode 100644
index 0000000000..0f98413f33
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNetError.js
@@ -0,0 +1,245 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const SSL3_PAGE = "https://ssl3.example.com/";
+const TLS10_PAGE = "https://tls1.example.com/";
+const TLS12_PAGE = "https://tls12.example.com/";
+const TRIPLEDES_PAGE = "https://3des.example.com/";
+
+const lazy = {};
+
+XPCOMUtils.defineLazyServiceGetter(
+  lazy,
+  "gDNSOverride",
+  "@mozilla.org/network/native-dns-override;1",
+  "nsINativeDNSResolverOverride"
+);
+
+// This includes all the cipher suite prefs we have.
+function resetPrefs() {
+  Services.prefs.clearUserPref("security.tls.version.min");
+  Services.prefs.clearUserPref("security.tls.version.max");
+  Services.prefs.clearUserPref("security.tls.version.enable-deprecated");
+  Services.prefs.clearUserPref("browser.fixup.alternate.enabled");
+}
+
+add_task(async function resetToDefaultConfig() {
+  info(
+    "Change TLS config to cause page load to fail, check that reset button is shown and that it works"
+  );
+
+  // Set ourselves up for a TLS error.
+  Services.prefs.setIntPref("security.tls.version.min", 1); // TLS 1.0
+  Services.prefs.setIntPref("security.tls.version.max", 1);
+
+  let browser;
+  let pageLoaded;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, TLS12_PAGE);
+      browser = gBrowser.selectedBrowser;
+      pageLoaded = BrowserTestUtils.waitForErrorPage(browser);
+    },
+    false
+  );
+
+  info("Loading and waiting for the net error");
+  await pageLoaded;
+
+  // Setup an observer for the target page.
+  const finalLoadComplete = BrowserTestUtils.browserLoaded(
+    browser,
+    false,
+    TLS12_PAGE
+  );
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    const doc = content.document;
+    ok(
+      doc.documentURI.startsWith("about:neterror"),
+      "Should be showing error page"
+    );
+
+    const prefResetButton = doc.getElementById("prefResetButton");
+    await ContentTaskUtils.waitForCondition(
+      () => ContentTaskUtils.is_visible(prefResetButton),
+      "prefResetButton is visible"
+    );
+
+    if (!Services.focus.focusedElement == prefResetButton) {
+      await ContentTaskUtils.waitForEvent(prefResetButton, "focus");
+    }
+
+    Assert.ok(true, "prefResetButton has focus");
+
+    prefResetButton.click();
+  });
+
+  info("Waiting for the page to load after the click");
+  await finalLoadComplete;
+
+  resetPrefs();
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+add_task(async function checkLearnMoreLink() {
+  info("Load an unsupported TLS page and check for a learn more link");
+
+  // Set ourselves up for TLS error
+  Services.prefs.setIntPref("security.tls.version.min", 3);
+  Services.prefs.setIntPref("security.tls.version.max", 4);
+
+  let browser;
+  let pageLoaded;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, TLS10_PAGE);
+      browser = gBrowser.selectedBrowser;
+      pageLoaded = BrowserTestUtils.waitForErrorPage(browser);
+    },
+    false
+  );
+
+  info("Loading and waiting for the net error");
+  await pageLoaded;
+
+  const baseURL = Services.urlFormatter.formatURLPref("app.support.baseURL");
+
+  await SpecialPowers.spawn(browser, [baseURL], function (_baseURL) {
+    const doc = content.document;
+    ok(
+      doc.documentURI.startsWith("about:neterror"),
+      "Should be showing error page"
+    );
+
+    const tlsVersionNotice = doc.getElementById("tlsVersionNotice");
+    ok(
+      ContentTaskUtils.is_visible(tlsVersionNotice),
+      "TLS version notice is visible"
+    );
+
+    const learnMoreLink = doc.getElementById("learnMoreLink");
+    ok(
+      ContentTaskUtils.is_visible(learnMoreLink),
+      "Learn More link is visible"
+    );
+    is(learnMoreLink.getAttribute("href"), _baseURL + "connection-not-secure");
+
+    const titleEl = doc.querySelector(".title-text");
+    const actualDataL10nID = titleEl.getAttribute("data-l10n-id");
+    is(
+      actualDataL10nID,
+      "nssFailure2-title",
+      "Correct error page title is set"
+    );
+
+    const errorCodeEl = doc.querySelector("#errorShortDesc2");
+    const actualDataL10Args = errorCodeEl.getAttribute("data-l10n-args");
+    ok(
+      actualDataL10Args.includes("SSL_ERROR_PROTOCOL_VERSION_ALERT"),
+      "Correct error code is set"
+    );
+  });
+
+  resetPrefs();
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+// When a user tries going to a host without a suffix
+// and the term doesn't match a host and we are able to suggest a
+// valid correction, the page should show the correction.
+// e.g. http://example/example2 -> https://www.example.com/example2
+add_task(async function checkDomainCorrection() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.fixup.alternate.enabled", false]],
+  });
+  lazy.gDNSOverride.addIPOverride("www.example.com", "::1");
+
+  info("Try loading a URI that should result in an error page");
+  BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    "http://example/example2/",
+    false
+  );
+
+  info("Loading and waiting for the net error");
+  let browser = gBrowser.selectedBrowser;
+  let pageLoaded = BrowserTestUtils.waitForErrorPage(browser);
+  await pageLoaded;
+
+  const baseURL = Services.urlFormatter.formatURLPref("app.support.baseURL");
+
+  await SpecialPowers.spawn(browser, [baseURL], async function (_baseURL) {
+    const doc = content.document;
+    ok(
+      doc.documentURI.startsWith("about:neterror"),
+      "Should be showing error page"
+    );
+
+    const errorNotice = doc.getElementById("errorShortDesc");
+    ok(ContentTaskUtils.is_visible(errorNotice), "Error text is visible");
+
+    // Wait for the domain suggestion to be resolved and for the text to update
+    let link;
+    await ContentTaskUtils.waitForCondition(() => {
+      link = errorNotice.querySelector("a");
+      return link && link.textContent != "";
+    }, "Helper link has been set");
+
+    is(
+      link.getAttribute("href"),
+      "https://www.example.com/example2/",
+      "Link was corrected"
+    );
+
+    const actualDataL10nID = link.getAttribute("data-l10n-name");
+    is(actualDataL10nID, "website", "Correct name is set");
+  });
+
+  lazy.gDNSOverride.clearHostOverride("www.example.com");
+  resetPrefs();
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+// Test that ciphersuites that use 3DES (namely, TLS_RSA_WITH_3DES_EDE_CBC_SHA)
+// can only be enabled when deprecated TLS is enabled.
+add_task(async function onlyAllow3DESWithDeprecatedTLS() {
+  // By default, connecting to a server that only uses 3DES should fail.
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:blank" },
+    async browser => {
+      BrowserTestUtils.loadURIString(browser, TRIPLEDES_PAGE);
+      await BrowserTestUtils.waitForErrorPage(browser);
+    }
+  );
+
+  // Enabling deprecated TLS should also enable 3DES.
+  Services.prefs.setBoolPref("security.tls.version.enable-deprecated", true);
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:blank" },
+    async browser => {
+      BrowserTestUtils.loadURIString(browser, TRIPLEDES_PAGE);
+      await BrowserTestUtils.browserLoaded(browser, false, TRIPLEDES_PAGE);
+    }
+  );
+
+  // 3DES can be disabled separately.
+  Services.prefs.setBoolPref(
+    "security.ssl3.deprecated.rsa_des_ede3_sha",
+    false
+  );
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:blank" },
+    async browser => {
+      BrowserTestUtils.loadURIString(browser, TRIPLEDES_PAGE);
+      await BrowserTestUtils.waitForErrorPage(browser);
+    }
+  );
+
+  resetPrefs();
+});
diff --git a/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js b/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js
new file mode 100644
index 0000000000..21e2ba7b51
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNetError_csp_iframe.js
@@ -0,0 +1,153 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const BLOCKED_PAGE =
+  // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+  "http://example.org:8000/browser/browser/base/content/test/about/csp_iframe.sjs";
+
+add_task(async function test_csp() {
+  let { iframePageTab, blockedPageTab } = await setupPage(
+    "iframe_page_csp.html",
+    BLOCKED_PAGE
+  );
+
+  let cspBrowser = gBrowser.selectedTab.linkedBrowser;
+
+  // The blocked page opened in a new window/tab
+  await SpecialPowers.spawn(
+    cspBrowser,
+    [BLOCKED_PAGE],
+    async function (cspBlockedPage) {
+      let cookieHeader = content.document.getElementById("strictCookie");
+      let location = content.document.location.href;
+
+      Assert.ok(
+        cookieHeader.textContent.includes("No same site strict cookie header"),
+        "Same site strict cookie has not been set"
+      );
+      Assert.equal(
+        location,
+        cspBlockedPage,
+        "Location of new page is correct!"
+      );
+    }
+  );
+
+  Services.cookies.removeAll();
+  BrowserTestUtils.removeTab(iframePageTab);
+  BrowserTestUtils.removeTab(blockedPageTab);
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+async function setupPage(htmlPageName, blockedPage) {
+  let iFramePage =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+      "http://example.com"
+    ) + htmlPageName;
+
+  // Opening the blocked page once in a new tab
+  let blockedPageTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    blockedPage
+  );
+  let blockedPageBrowser = blockedPageTab.linkedBrowser;
+
+  let cookies = Services.cookies.getCookiesFromHost(
+    "example.org",
+    blockedPageBrowser.contentPrincipal.originAttributes
+  );
+  let strictCookie = cookies[0];
+
+  is(
+    strictCookie.value,
+    "green",
+    "Same site strict cookie has the expected value"
+  );
+
+  is(strictCookie.sameSite, 2, "The cookie is a same site strict cookie");
+
+  // Opening the page that contains the iframe
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
+  let browser = tab.linkedBrowser;
+  let browserLoaded = BrowserTestUtils.browserLoaded(
+    browser,
+    true,
+    blockedPage,
+    true
+  );
+
+  BrowserTestUtils.loadURIString(browser, iFramePage);
+  await browserLoaded;
+  info("The error page has loaded!");
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let iframe = content.document.getElementById("theIframe");
+
+    await ContentTaskUtils.waitForCondition(() =>
+      SpecialPowers.spawn(iframe, [], () =>
+        content.document.body.classList.contains("neterror")
+      )
+    );
+  });
+
+  let iframe = browser.browsingContext.children[0];
+
+  let newTabLoaded = BrowserTestUtils.waitForNewTab(gBrowser, null, true);
+
+  // In the iframe, we see the correct error page and click on the button
+  // to open the blocked page in a new window/tab
+  await SpecialPowers.spawn(iframe, [], async function () {
+    let doc = content.document;
+
+    // aboutNetError.mjs is using async localization to format several
+    // messages and in result the translation may be applied later.
+    // We want to return the textContent of the element only after
+    // the translation completes, so let's wait for it here.
+    let elements = [
+      doc.getElementById("errorLongDesc"),
+      doc.getElementById("openInNewWindowButton"),
+    ];
+    await ContentTaskUtils.waitForCondition(() => {
+      return elements.every(elem => !!elem.textContent.trim().length);
+    });
+
+    let textLongDescription = doc.getElementById("errorLongDesc").textContent;
+    let learnMoreLinkLocation = doc.getElementById("learnMoreLink").href;
+
+    Assert.ok(
+      textLongDescription.includes(
+        "To see this page, you need to open it in a new window."
+      ),
+      "Correct error message found"
+    );
+
+    let button = doc.getElementById("openInNewWindowButton");
+    Assert.ok(
+      button.textContent.includes("Open Site in New Window"),
+      "We see the correct button to open the site in a new window"
+    );
+
+    Assert.ok(
+      learnMoreLinkLocation.includes("xframe-neterror-page"),
+      "Correct Learn More URL for CSP error page"
+    );
+
+    // We click on the button
+    await EventUtils.synthesizeMouseAtCenter(button, {}, content);
+  });
+  info("Button was clicked!");
+
+  // We wait for the new tab to load
+  await newTabLoaded;
+  info("The new tab has loaded!");
+
+  let iframePageTab = tab;
+  return {
+    iframePageTab,
+    blockedPageTab,
+  };
+}
diff --git a/browser/base/content/test/about/browser_aboutNetError_native_fallback.js b/browser/base/content/test/about/browser_aboutNetError_native_fallback.js
new file mode 100644
index 0000000000..4a87ad5cce
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNetError_native_fallback.js
@@ -0,0 +1,174 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+let oldProxyType = Services.prefs.getIntPref("network.proxy.type");
+
+function reset() {
+  Services.prefs.clearUserPref("network.trr.display_fallback_warning");
+  Services.prefs.clearUserPref("network.trr.mode");
+  Services.prefs.clearUserPref("network.dns.native-is-localhost");
+  Services.prefs.clearUserPref("doh-rollout.disable-heuristics");
+  Services.prefs.setIntPref("network.proxy.type", oldProxyType);
+  Services.prefs.clearUserPref("network.trr.uri");
+
+  Services.dns.setHeuristicDetectionResult(Ci.nsITRRSkipReason.TRR_OK);
+}
+
+// This helper verifies that the given url loads correctly
+async function verifyLoad(url, testName) {
+  let browser;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, url);
+      browser = gBrowser.selectedBrowser;
+    },
+    true
+  );
+
+  await SpecialPowers.spawn(browser, [{ url, testName }], function (args) {
+    const doc = content.document;
+    ok(
+      doc.documentURI == args.url,
+      "Should have loaded page: " + args.testName
+    );
+  });
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+}
+
+// This helper verifies that loading the given url will lead to an error -- the fallback warning if the parameter is true
+async function verifyError(url, fallbackWarning, testName) {
+  // Clear everything.
+  Services.telemetry.clearEvents();
+  await TestUtils.waitForCondition(() => {
+    let events = Services.telemetry.snapshotEvents(
+      Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+      true
+    ).content;
+    return !events || !events.length;
+  });
+  Services.telemetry.setEventRecordingEnabled("security.doh.neterror", true);
+
+  let browser;
+  let pageLoaded;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, url);
+      browser = gBrowser.selectedBrowser;
+      pageLoaded = BrowserTestUtils.waitForErrorPage(browser);
+    },
+    false
+  );
+
+  info("Loading and waiting for the net error");
+  await pageLoaded;
+
+  await SpecialPowers.spawn(
+    browser,
+    [{ url, fallbackWarning, testName }],
+    function (args) {
+      const doc = content.document;
+
+      ok(doc.documentURI.startsWith("about:neterror"));
+      "Should be showing error page: " + args.testName;
+
+      const titleEl = doc.querySelector(".title-text");
+      const actualDataL10nID = titleEl.getAttribute("data-l10n-id");
+      if (args.fallbackWarning) {
+        is(
+          actualDataL10nID,
+          "dns-not-found-native-fallback-title2",
+          "Correct fallback warning error page title is set: " + args.testName
+        );
+      } else {
+        ok(
+          actualDataL10nID != "dns-not-found-native-fallback-title2",
+          "Should not show fallback warning: " + args.testName
+        );
+      }
+    }
+  );
+
+  if (fallbackWarning) {
+    let loadEvent = await TestUtils.waitForCondition(() => {
+      let events = Services.telemetry.snapshotEvents(
+        Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+        true
+      ).content;
+      return events?.find(
+        e => e[1] == "security.doh.neterror" && e[2] == "load"
+      );
+    }, "recorded telemetry for the load");
+    loadEvent.shift();
+    Assert.deepEqual(loadEvent, [
+      "security.doh.neterror",
+      "load",
+      "dohwarning",
+      "NativeFallbackWarning",
+      {
+        mode: "0",
+        provider_key: "0.0.0.0",
+        skip_reason: "TRR_HEURISTIC_TRIPPED_CANARY",
+      },
+    ]);
+  }
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+}
+
+// This test verifies that the native fallback warning appears in the desired scenarios, and only in those scenarios
+add_task(async function nativeFallbackWarnings() {
+  Services.prefs.setBoolPref("network.dns.native-is-localhost", true);
+
+  // Disable heuristics since they will attempt to connect to external servers
+  Services.prefs.setBoolPref("doh-rollout.disable-heuristics", true);
+
+  // Set a local TRR to prevent external connections
+  Services.prefs.setCharPref("network.trr.uri", "https://0.0.0.0/dns-query");
+
+  registerCleanupFunction(reset);
+
+  // Test without DoH
+  Services.prefs.setIntPref(
+    "network.trr.mode",
+    Ci.nsIDNSService.MODE_NATIVEONLY
+  );
+
+  Services.dns.clearCache(true);
+  await verifyLoad("https://www.example.com/", "valid url, no error");
+
+  // Should not trigger the native fallback warning
+  await verifyError("https://does-not-exist.test", false, "non existent url");
+
+  // We need to disable proxy, otherwise TRR isn't used for name resolution.
+  Services.prefs.setIntPref("network.proxy.type", 0);
+
+  // Switch to TRR first
+  Services.prefs.setIntPref(
+    "network.trr.mode",
+    Ci.nsIDNSService.MODE_NATIVEONLY
+  );
+  Services.prefs.setBoolPref("network.trr.display_fallback_warning", true);
+
+  // Simulate a tripped canary network
+  Services.dns.setHeuristicDetectionResult(
+    Ci.nsITRRSkipReason.TRR_HEURISTIC_TRIPPED_CANARY
+  );
+
+  // We should see the fallback warning displayed in both of these scenarios
+  Services.dns.clearCache(true);
+  await verifyError(
+    "https://www.example.com",
+    true,
+    "canary heuristic tripped"
+  );
+  await verifyError(
+    "https://does-not-exist.test",
+    true,
+    "canary heuristic tripped - non existent url"
+  );
+
+  reset();
+});
diff --git a/browser/base/content/test/about/browser_aboutNetError_trr.js b/browser/base/content/test/about/browser_aboutNetError_trr.js
new file mode 100644
index 0000000000..bfee686e7c
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNetError_trr.js
@@ -0,0 +1,189 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// See bug 1831731. This test should not actually try to create a connection to
+// the real DoH endpoint. But that may happen when clearing the proxy type, and
+// sometimes even in the next test.
+// To prevent that we override the IP to a local address.
+Cc["@mozilla.org/network/native-dns-override;1"]
+  .getService(Ci.nsINativeDNSResolverOverride)
+  .addIPOverride("mozilla.cloudflare-dns.com", "127.0.0.1");
+
+let oldProxyType = Services.prefs.getIntPref("network.proxy.type");
+function resetPrefs() {
+  Services.prefs.clearUserPref("network.trr.mode");
+  Services.prefs.clearUserPref("network.dns.native-is-localhost");
+  Services.prefs.setIntPref("network.proxy.type", oldProxyType);
+}
+
+async function loadErrorPage() {
+  Services.prefs.setBoolPref("network.dns.native-is-localhost", true);
+  Services.prefs.setIntPref("network.trr.mode", Ci.nsIDNSService.MODE_TRRONLY);
+  // We need to disable proxy, otherwise TRR isn't used for name resolution.
+  Services.prefs.setIntPref("network.proxy.type", 0);
+  registerCleanupFunction(resetPrefs);
+
+  let browser;
+  let pageLoaded;
+  await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    () => {
+      gBrowser.selectedTab = BrowserTestUtils.addTab(
+        gBrowser,
+        "https://does-not-exist.test"
+      );
+      browser = gBrowser.selectedBrowser;
+      pageLoaded = BrowserTestUtils.waitForErrorPage(browser);
+    },
+    false
+  );
+
+  info("Loading and waiting for the net error");
+  await pageLoaded;
+  return browser;
+}
+
+// This test makes sure that the Add exception button only shows up
+// when the skipReason indicates that the domain could not be resolved.
+// If instead there is a problem with the TRR connection, then we don't
+// show the exception button.
+add_task(async function exceptionButtonTRROnly() {
+  let browser = await loadErrorPage();
+
+  await SpecialPowers.spawn(browser, [], function () {
+    const doc = content.document;
+    ok(
+      doc.documentURI.startsWith("about:neterror"),
+      "Should be showing error page"
+    );
+
+    const titleEl = doc.querySelector(".title-text");
+    const actualDataL10nID = titleEl.getAttribute("data-l10n-id");
+    is(
+      actualDataL10nID,
+      "dns-not-found-trr-only-title2",
+      "Correct error page title is set"
+    );
+
+    let trrExceptionButton = doc.getElementById("trrExceptionButton");
+    Assert.equal(
+      trrExceptionButton.hidden,
+      true,
+      "Exception button should be hidden for TRR service failures"
+    );
+  });
+
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+  resetPrefs();
+});
+
+add_task(async function TRROnlyExceptionButtonTelemetry() {
+  // Clear everything.
+  Services.telemetry.clearEvents();
+  await TestUtils.waitForCondition(() => {
+    let events = Services.telemetry.snapshotEvents(
+      Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+      true
+    ).content;
+    return !events || !events.length;
+  });
+  Services.telemetry.setEventRecordingEnabled("security.doh.neterror", true);
+
+  let browser = await loadErrorPage();
+
+  await SpecialPowers.spawn(browser, [], function () {
+    const doc = content.document;
+    ok(
+      doc.documentURI.startsWith("about:neterror"),
+      "Should be showing error page"
+    );
+  });
+
+  let loadEvent = await TestUtils.waitForCondition(() => {
+    let events = Services.telemetry.snapshotEvents(
+      Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+      true
+    ).content;
+    return events?.find(e => e[1] == "security.doh.neterror" && e[2] == "load");
+  }, "recorded telemetry for the load");
+
+  loadEvent.shift();
+  Assert.deepEqual(loadEvent, [
+    "security.doh.neterror",
+    "load",
+    "dohwarning",
+    "TRROnlyFailure",
+    {
+      mode: "3",
+      provider_key: "mozilla.cloudflare-dns.com",
+      skip_reason: "TRR_UNKNOWN_CHANNEL_FAILURE",
+    },
+  ]);
+
+  await SpecialPowers.spawn(browser, [], function () {
+    const doc = content.document;
+    let buttons = ["neterrorTryAgainButton", "trrSettingsButton"];
+    for (let buttonId of buttons) {
+      let button = doc.getElementById(buttonId);
+      button.click();
+    }
+  });
+
+  // Since we click TryAgain, make sure the error page is loaded again.
+  await BrowserTestUtils.waitForErrorPage(browser);
+
+  is(
+    gBrowser.tabs.length,
+    3,
+    "Should open about:preferences#privacy-doh in another tab"
+  );
+
+  let clickEvents = await TestUtils.waitForCondition(
+    () => {
+      let events = Services.telemetry.snapshotEvents(
+        Ci.nsITelemetry.DATASET_PRERELEASE_CHANNELS,
+        true
+      ).content;
+      return events?.filter(
+        e => e[1] == "security.doh.neterror" && e[2] == "click"
+      );
+    },
+    "recorded telemetry for clicking buttons",
+    500,
+    100
+  );
+
+  let firstEvent = clickEvents[0];
+  firstEvent.shift(); // remove timestamp
+  Assert.deepEqual(firstEvent, [
+    "security.doh.neterror",
+    "click",
+    "try_again_button",
+    "TRROnlyFailure",
+    {
+      mode: "3",
+      provider_key: "mozilla.cloudflare-dns.com",
+      skip_reason: "TRR_UNKNOWN_CHANNEL_FAILURE",
+    },
+  ]);
+
+  let secondEvent = clickEvents[1];
+  secondEvent.shift(); // remove timestamp
+  Assert.deepEqual(secondEvent, [
+    "security.doh.neterror",
+    "click",
+    "settings_button",
+    "TRROnlyFailure",
+    {
+      mode: "3",
+      provider_key: "mozilla.cloudflare-dns.com",
+      skip_reason: "TRR_UNKNOWN_CHANNEL_FAILURE",
+    },
+  ]);
+
+  BrowserTestUtils.removeTab(gBrowser.tabs[2]);
+  BrowserTestUtils.removeTab(gBrowser.tabs[1]);
+  resetPrefs();
+});
diff --git a/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js b/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js
new file mode 100644
index 0000000000..ae4d5c22a2
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNetError_xfo_iframe.js
@@ -0,0 +1,139 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const BLOCKED_PAGE =
+  // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+  "http://example.org:8000/browser/browser/base/content/test/about/xfo_iframe.sjs";
+
+add_task(async function test_xfo_iframe() {
+  let { iframePageTab, blockedPageTab } = await setupPage(
+    "iframe_page_xfo.html",
+    BLOCKED_PAGE
+  );
+
+  let xfoBrowser = gBrowser.selectedTab.linkedBrowser;
+
+  // The blocked page opened in a new window/tab
+  await SpecialPowers.spawn(
+    xfoBrowser,
+    [BLOCKED_PAGE],
+    async function (xfoBlockedPage) {
+      let cookieHeader = content.document.getElementById("strictCookie");
+      let location = content.document.location.href;
+
+      Assert.ok(
+        cookieHeader.textContent.includes("No same site strict cookie header"),
+        "Same site strict cookie has not been set"
+      );
+      Assert.equal(
+        location,
+        xfoBlockedPage,
+        "Location of new page is correct!"
+      );
+    }
+  );
+
+  Services.cookies.removeAll();
+  BrowserTestUtils.removeTab(iframePageTab);
+  BrowserTestUtils.removeTab(blockedPageTab);
+  BrowserTestUtils.removeTab(gBrowser.selectedTab);
+});
+
+async function setupPage(htmlPageName, blockedPage) {
+  let iFramePage =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+      "http://example.com"
+    ) + htmlPageName;
+
+  // Opening the blocked page once in a new tab
+  let blockedPageTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    blockedPage
+  );
+  let blockedPageBrowser = blockedPageTab.linkedBrowser;
+
+  let cookies = Services.cookies.getCookiesFromHost(
+    "example.org",
+    blockedPageBrowser.contentPrincipal.originAttributes
+  );
+  let strictCookie = cookies[0];
+
+  is(
+    strictCookie.value,
+    "creamy",
+    "Same site strict cookie has the expected value"
+  );
+
+  is(strictCookie.sameSite, 2, "The cookie is a same site strict cookie");
+
+  // Opening the page that contains the iframe
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
+  let browser = tab.linkedBrowser;
+  let browserLoaded = BrowserTestUtils.browserLoaded(
+    browser,
+    true,
+    blockedPage,
+    true
+  );
+
+  BrowserTestUtils.loadURIString(browser, iFramePage);
+  await browserLoaded;
+  info("The error page has loaded!");
+
+  await SpecialPowers.spawn(browser, [], async function () {
+    let iframe = content.document.getElementById("theIframe");
+
+    await ContentTaskUtils.waitForCondition(() =>
+      SpecialPowers.spawn(iframe, [], () =>
+        content.document.body.classList.contains("neterror")
+      )
+    );
+  });
+
+  let frameContext = browser.browsingContext.children[0];
+  let newTabLoaded = BrowserTestUtils.waitForNewTab(gBrowser, null, true);
+
+  // In the iframe, we see the correct error page and click on the button
+  // to open the blocked page in a new window/tab
+  await SpecialPowers.spawn(frameContext, [], async function () {
+    let doc = content.document;
+    let textLongDescription = doc.getElementById("errorLongDesc").textContent;
+    let learnMoreLinkLocation = doc.getElementById("learnMoreLink").href;
+
+    Assert.ok(
+      textLongDescription.includes(
+        "To see this page, you need to open it in a new window."
+      ),
+      "Correct error message found"
+    );
+
+    let button = doc.getElementById("openInNewWindowButton");
+    Assert.ok(
+      button.textContent.includes("Open Site in New Window"),
+      "We see the correct button to open the site in a new window"
+    );
+
+    Assert.ok(
+      learnMoreLinkLocation.includes("xframe-neterror-page"),
+      "Correct Learn More URL for XFO error page"
+    );
+
+    // We click on the button
+    await EventUtils.synthesizeMouseAtCenter(button, {}, content);
+  });
+  info("Button was clicked!");
+
+  // We wait for the new tab to load
+  await newTabLoaded;
+  info("The new tab has loaded!");
+
+  let iframePageTab = tab;
+  return {
+    iframePageTab,
+    blockedPageTab,
+  };
+}
diff --git a/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbar.js b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbar.js
new file mode 100644
index 0000000000..c566276d9f
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbar.js
@@ -0,0 +1,311 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function bookmarks_toolbar_shown_on_newtab() {
+  let newtab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:newtab",
+    waitForLoad: false,
+  });
+
+  // 1: Test that the toolbar is shown in a newly opened foreground about:newtab
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar should be visible on newtab",
+  });
+  ok(isBookmarksToolbarVisible(), "Toolbar should be visible on newtab");
+
+  // 2: Test that the toolbar is hidden when the browser is navigated away from newtab
+  BrowserTestUtils.loadURIString(newtab.linkedBrowser, "https://example.com");
+  await BrowserTestUtils.browserLoaded(newtab.linkedBrowser);
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message:
+      "Toolbar should not be visible on newtab after example.com is loaded within",
+  });
+  ok(
+    !isBookmarksToolbarVisible(),
+    "Toolbar should not be visible on newtab after example.com is loaded within"
+  );
+
+  // 3: Re-load about:newtab in the browser for the following tests and confirm toolbar reappears
+  BrowserTestUtils.loadURIString(newtab.linkedBrowser, "about:newtab");
+  await BrowserTestUtils.browserLoaded(newtab.linkedBrowser);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar should be visible on newtab",
+  });
+  ok(isBookmarksToolbarVisible(), "Toolbar should be visible on newtab");
+
+  // 4: Toolbar should get hidden when opening a new tab to example.com
+  let example = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "https://example.com",
+  });
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message: "Toolbar should be hidden on example.com",
+  });
+
+  // 5: Toolbar should become visible when switching tabs to newtab
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible with switch to newtab",
+  });
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible with switch to newtab");
+
+  // 6: Toolbar should become hidden when switching tabs to example.com
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message: "Toolbar is hidden with switch to example",
+  });
+
+  // 7: Similar to #3 above, loading about:newtab in example should show toolbar
+  BrowserTestUtils.loadURIString(example.linkedBrowser, "about:newtab");
+  await BrowserTestUtils.browserLoaded(example.linkedBrowser);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible with newtab load",
+  });
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible with newtab load");
+
+  // 8: Switching back and forth between two browsers showing about:newtab will still show the toolbar
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible with switch to newtab");
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  ok(
+    isBookmarksToolbarVisible(),
+    "Toolbar is visible with switch to example(newtab)"
+  );
+
+  // 9: With custom newtab URL, toolbar isn't shown on about:newtab but is shown on custom URL
+  let oldNewTab = AboutNewTab.newTabURL;
+  AboutNewTab.newTabURL = "https://example.com/2";
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({ visible: false });
+  ok(!isBookmarksToolbarVisible(), "Toolbar should hide with custom newtab");
+  BrowserTestUtils.loadURIString(example.linkedBrowser, AboutNewTab.newTabURL);
+  await BrowserTestUtils.browserLoaded(example.linkedBrowser);
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await waitForBookmarksToolbarVisibility({ visible: true });
+  ok(
+    isBookmarksToolbarVisible(),
+    "Toolbar is visible with switch to custom newtab"
+  );
+
+  await BrowserTestUtils.removeTab(newtab);
+  await BrowserTestUtils.removeTab(example);
+  AboutNewTab.newTabURL = oldNewTab;
+});
+
+add_task(async function bookmarks_toolbar_open_persisted() {
+  let newtab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:newtab",
+    waitForLoad: false,
+  });
+  let example = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "https://example.com",
+  });
+  let isToolbarPersistedOpen = () =>
+    Services.prefs.getCharPref("browser.toolbars.bookmarks.visibility") ==
+    "always";
+
+  ok(!isBookmarksToolbarVisible(), "Toolbar is hidden");
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({ visible: true });
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible");
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await waitForBookmarksToolbarVisibility({ visible: false });
+  ok(!isBookmarksToolbarVisible(), "Toolbar is hidden");
+  ok(!isToolbarPersistedOpen(), "Toolbar is not persisted open");
+
+  let contextMenu = document.querySelector("#toolbar-context-menu");
+  let popupShown = BrowserTestUtils.waitForEvent(contextMenu, "popupshown");
+  let menuButton = document.getElementById("PanelUI-menu-button");
+  EventUtils.synthesizeMouseAtCenter(
+    menuButton,
+    { type: "contextmenu" },
+    window
+  );
+  await popupShown;
+  let bookmarksToolbarMenu = document.querySelector("#toggle_PersonalToolbar");
+  let subMenu = bookmarksToolbarMenu.querySelector("menupopup");
+  popupShown = BrowserTestUtils.waitForEvent(subMenu, "popupshown");
+  bookmarksToolbarMenu.openMenu(true);
+  await popupShown;
+  let alwaysMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="always"]'
+  );
+  let neverMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="never"]'
+  );
+  let newTabMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="newtab"]'
+  );
+  is(alwaysMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  is(neverMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  is(newTabMenuItem.getAttribute("checked"), "true", "Menuitem is checked");
+
+  subMenu.activateItem(alwaysMenuItem);
+
+  await waitForBookmarksToolbarVisibility({ visible: true });
+  popupShown = BrowserTestUtils.waitForEvent(contextMenu, "popupshown");
+  EventUtils.synthesizeMouseAtCenter(
+    menuButton,
+    { type: "contextmenu" },
+    window
+  );
+  await popupShown;
+  bookmarksToolbarMenu = document.querySelector("#toggle_PersonalToolbar");
+  subMenu = bookmarksToolbarMenu.querySelector("menupopup");
+  popupShown = BrowserTestUtils.waitForEvent(subMenu, "popupshown");
+  bookmarksToolbarMenu.openMenu(true);
+  await popupShown;
+  alwaysMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="always"]'
+  );
+  neverMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="never"]'
+  );
+  newTabMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="newtab"]'
+  );
+  is(alwaysMenuItem.getAttribute("checked"), "true", "Menuitem is checked");
+  is(neverMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  is(newTabMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  contextMenu.hidePopup();
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible");
+  ok(isToolbarPersistedOpen(), "Toolbar is persisted open");
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible");
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  ok(isBookmarksToolbarVisible(), "Toolbar is visible");
+
+  popupShown = BrowserTestUtils.waitForEvent(contextMenu, "popupshown");
+  EventUtils.synthesizeMouseAtCenter(
+    menuButton,
+    { type: "contextmenu" },
+    window
+  );
+  await popupShown;
+  bookmarksToolbarMenu = document.querySelector("#toggle_PersonalToolbar");
+  subMenu = bookmarksToolbarMenu.querySelector("menupopup");
+  popupShown = BrowserTestUtils.waitForEvent(subMenu, "popupshown");
+  bookmarksToolbarMenu.openMenu(true);
+  await popupShown;
+  alwaysMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="always"]'
+  );
+  neverMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="never"]'
+  );
+  newTabMenuItem = document.querySelector(
+    'menuitem[data-visibility-enum="newtab"]'
+  );
+  is(alwaysMenuItem.getAttribute("checked"), "true", "Menuitem is checked");
+  is(neverMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  is(newTabMenuItem.getAttribute("checked"), "false", "Menuitem isn't checked");
+  subMenu.activateItem(newTabMenuItem);
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message: "Toolbar is hidden",
+  });
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible",
+  });
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message: "Toolbar is hidden",
+  });
+
+  await BrowserTestUtils.removeTab(newtab);
+  await BrowserTestUtils.removeTab(example);
+});
+
+add_task(async function test_with_newtabpage_disabled() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.newtabpage.enabled", true]],
+  });
+
+  let tabCount = gBrowser.tabs.length;
+  document.getElementById("cmd_newNavigatorTab").doCommand();
+  // Can't use BrowserTestUtils.waitForNewTab since onLocationChange will not
+  // fire due to preloaded new tabs.
+  await TestUtils.waitForCondition(() => gBrowser.tabs.length == tabCount + 1);
+  let newtab = gBrowser.selectedTab;
+  is(newtab.linkedBrowser.currentURI.spec, "about:newtab", "newtab is loaded");
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible with NTP enabled",
+  });
+  let firstid = await SpecialPowers.spawn(newtab.linkedBrowser, [], () => {
+    return content.document.body.firstElementChild?.id;
+  });
+  is(firstid, "root", "new tab page contains content");
+  await BrowserTestUtils.removeTab(newtab);
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.newtabpage.enabled", false]],
+  });
+
+  document.getElementById("cmd_newNavigatorTab").doCommand();
+  await TestUtils.waitForCondition(() => gBrowser.tabs.length == tabCount + 1);
+  newtab = gBrowser.selectedTab;
+
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible with NTP disabled",
+  });
+
+  is(
+    newtab.linkedBrowser.currentURI.spec,
+    "about:newtab",
+    "blank new tab is loaded"
+  );
+  firstid = await SpecialPowers.spawn(newtab.linkedBrowser, [], () => {
+    return content.document.body.firstElementChild;
+  });
+  ok(!firstid, "blank new tab page contains no content");
+
+  await BrowserTestUtils.removeTab(newtab);
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.newtabpage.enabled", true]],
+  });
+});
+
+add_task(async function test_history_pushstate() {
+  await BrowserTestUtils.withNewTab("https://example.com/", async browser => {
+    await waitForBookmarksToolbarVisibility({ visible: false });
+    ok(!isBookmarksToolbarVisible(), "Toolbar should be hidden");
+
+    // Temporarily show the toolbar:
+    setToolbarVisibility(
+      document.querySelector("#PersonalToolbar"),
+      true,
+      false,
+      false
+    );
+    ok(isBookmarksToolbarVisible(), "Toolbar should now be visible");
+
+    // Now "navigate"
+    await SpecialPowers.spawn(browser, [], () => {
+      content.location.href += "#foo";
+    });
+
+    await TestUtils.waitForCondition(
+      () => gURLBar.value.endsWith("#foo"),
+      "URL bar should update"
+    );
+    ok(isBookmarksToolbarVisible(), "Toolbar should still be visible");
+  });
+});
diff --git a/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarEmpty.js b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarEmpty.js
new file mode 100644
index 0000000000..8e9ef8d163
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarEmpty.js
@@ -0,0 +1,158 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const bookmarksInfo = [
+  {
+    title: "firefox",
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    url: "http://example.com",
+  },
+  {
+    title: "rules",
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    url: "http://example.com/2",
+  },
+  {
+    title: "yo",
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    url: "http://example.com/2",
+  },
+];
+
+add_setup(async function () {
+  await SpecialPowers.pushPrefEnv({
+    // Ensure we can wait for about:newtab to load.
+    set: [["browser.newtab.preload", false]],
+  });
+  // Move all existing bookmarks in the Bookmarks Toolbar and
+  // Other Bookmarks to the Bookmarks Menu so they don't affect
+  // the visibility of the Bookmarks Toolbar. Restore them at
+  // the end of the test.
+  let Bookmarks = PlacesUtils.bookmarks;
+  let toolbarBookmarks = [];
+  let unfiledBookmarks = [];
+  let guidBookmarkTuples = [
+    [Bookmarks.toolbarGuid, toolbarBookmarks],
+    [Bookmarks.unfiledGuid, unfiledBookmarks],
+  ];
+  for (let [parentGuid, arr] of guidBookmarkTuples) {
+    await Bookmarks.fetch({ parentGuid }, bookmark => arr.push(bookmark));
+  }
+  await Promise.all(
+    [...toolbarBookmarks, ...unfiledBookmarks].map(async bookmark => {
+      bookmark.parentGuid = Bookmarks.menuGuid;
+      return Bookmarks.update(bookmark);
+    })
+  );
+  registerCleanupFunction(async () => {
+    for (let [parentGuid, arr] of guidBookmarkTuples) {
+      await Promise.all(
+        arr.map(async bookmark => {
+          bookmark.parentGuid = parentGuid;
+          return Bookmarks.update(bookmark);
+        })
+      );
+    }
+  });
+});
+
+add_task(async function bookmarks_toolbar_not_shown_when_empty() {
+  let bookmarks = await PlacesUtils.bookmarks.insertTree({
+    guid: PlacesUtils.bookmarks.toolbarGuid,
+    children: bookmarksInfo,
+  });
+  let example = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "https://example.com",
+  });
+  let newtab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:newtab",
+  });
+  let emptyMessage = document.getElementById("personal-toolbar-empty");
+
+  // 1: Test that the toolbar is shown in a newly opened foreground about:newtab
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar should be visible on newtab",
+  });
+  ok(emptyMessage.hidden, "Empty message is hidden with toolbar populated");
+
+  // 2: Toolbar should get hidden when switching tab to example.com
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await waitForBookmarksToolbarVisibility({
+    visible: false,
+    message: "Toolbar should be hidden on example.com",
+  });
+
+  // 3: Remove all children of the Bookmarks Toolbar and confirm that
+  // the toolbar should not become visible when switching to newtab
+  CustomizableUI.addWidgetToArea(
+    "personal-bookmarks",
+    CustomizableUI.AREA_TABSTRIP
+  );
+  CustomizableUI.removeWidgetFromArea("import-button");
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible when there are no items in the toolbar area",
+  });
+  ok(!emptyMessage.hidden, "Empty message is shown with toolbar empty");
+  // Click the link and check we open the library:
+  let winPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+  EventUtils.synthesizeMouseAtCenter(
+    emptyMessage.querySelector(".text-link"),
+    {}
+  );
+  let libraryWin = await winPromise;
+  is(
+    libraryWin.document.location.href,
+    "chrome://browser/content/places/places.xhtml",
+    "Should have opened library."
+  );
+  await BrowserTestUtils.closeWindow(libraryWin);
+
+  // 4: Put personal-bookmarks back in the toolbar and confirm the toolbar is visible now
+  CustomizableUI.addWidgetToArea(
+    "personal-bookmarks",
+    CustomizableUI.AREA_BOOKMARKS
+  );
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar should be visible with Bookmarks Toolbar Items restored",
+  });
+  ok(emptyMessage.hidden, "Empty message is hidden with toolbar populated");
+
+  // 5: Remove all the bookmarks in the toolbar and confirm that the toolbar
+  // is hidden on the New Tab now
+  await PlacesUtils.bookmarks.remove(bookmarks);
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message:
+      "Toolbar is visible when there are no items or nested bookmarks in the toolbar area",
+  });
+  ok(!emptyMessage.hidden, "Empty message is shown with toolbar empty");
+
+  // 6: Add a toolbarbutton and make sure that the toolbar appears when the button is visible
+  CustomizableUI.addWidgetToArea(
+    "characterencoding-button",
+    CustomizableUI.AREA_BOOKMARKS
+  );
+  await BrowserTestUtils.switchTab(gBrowser, example);
+  await BrowserTestUtils.switchTab(gBrowser, newtab);
+  await waitForBookmarksToolbarVisibility({
+    visible: true,
+    message: "Toolbar is visible when there is a visible button in the toolbar",
+  });
+  ok(emptyMessage.hidden, "Empty message is hidden with button in toolbar");
+
+  await BrowserTestUtils.removeTab(newtab);
+  await BrowserTestUtils.removeTab(example);
+  CustomizableUI.reset();
+});
diff --git a/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarNewWindow.js b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarNewWindow.js
new file mode 100644
index 0000000000..19c990bbbc
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarNewWindow.js
@@ -0,0 +1,82 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+requestLongerTimeout(2);
+
+const testCases = [
+  {
+    name: "bookmarks_toolbar_shown_on_newtab_newTabEnabled",
+    newTabEnabled: true,
+  },
+  {
+    name: "bookmarks_toolbar_shown_on_newtab",
+    newTabEnabled: false,
+  },
+];
+
+async function test_bookmarks_toolbar_visibility({ newTabEnabled }) {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.newtabpage.enabled", newTabEnabled]],
+  });
+
+  // Ensure the toolbar doesnt become visible at any point before the tab finishes loading
+
+  let url =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      "https://example.com"
+    ) + "slow_loading_page.sjs";
+
+  let startTime = Date.now();
+  let newWindowOpened = BrowserTestUtils.domWindowOpened();
+  let beforeShown = TestUtils.topicObserved("browser-window-before-show");
+
+  openTrustedLinkIn(url, "window");
+
+  let newWin = await newWindowOpened;
+  let slowSiteLoaded = BrowserTestUtils.firstBrowserLoaded(newWin, false);
+
+  function checkToolbarIsCollapsed(win, message) {
+    let toolbar = win.document.getElementById("PersonalToolbar");
+    ok(toolbar && toolbar.collapsed, message);
+  }
+
+  await beforeShown;
+  checkToolbarIsCollapsed(
+    newWin,
+    "Toolbar is initially hidden on the new window"
+  );
+
+  function onToolbarMutation() {
+    checkToolbarIsCollapsed(newWin, "Toolbar should remain collapsed");
+  }
+  let toolbarMutationObserver = new newWin.MutationObserver(onToolbarMutation);
+  toolbarMutationObserver.observe(
+    newWin.document.getElementById("PersonalToolbar"),
+    {
+      attributeFilter: ["collapsed"],
+    }
+  );
+
+  info("Waiting for the slow site to load");
+  await slowSiteLoaded;
+  info(`Window opened and slow site loaded in: ${Date.now() - startTime}ms`);
+
+  checkToolbarIsCollapsed(newWin, "Finally, the toolbar is still hidden");
+
+  toolbarMutationObserver.disconnect();
+  await BrowserTestUtils.closeWindow(newWin);
+}
+
+// Make separate tasks for each test case, so we get more useful stack traces on failure
+for (let testData of testCases) {
+  let tmp = {
+    async [testData.name]() {
+      info("testing with: " + JSON.stringify(testData));
+      await test_bookmarks_toolbar_visibility(testData);
+    },
+  };
+  add_task(tmp[testData.name]);
+}
diff --git a/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarPrefs.js b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarPrefs.js
new file mode 100644
index 0000000000..e9f7768beb
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutNewTab_bookmarksToolbarPrefs.js
@@ -0,0 +1,74 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+requestLongerTimeout(3);
+
+add_task(async function test_with_different_pref_states() {
+  // [prefName, prefValue, toolbarVisibleExampleCom, toolbarVisibleNewTab]
+  let bookmarksToolbarVisibilityStates = [
+    ["browser.toolbars.bookmarks.visibility", "newtab"],
+    ["browser.toolbars.bookmarks.visibility", "always"],
+    ["browser.toolbars.bookmarks.visibility", "never"],
+  ];
+  for (let visibilityState of bookmarksToolbarVisibilityStates) {
+    await SpecialPowers.pushPrefEnv({
+      set: [visibilityState],
+    });
+
+    for (let privateWin of [true, false]) {
+      info(
+        `Testing with ${visibilityState} in a ${
+          privateWin ? "private" : "non-private"
+        } window`
+      );
+      let win = await BrowserTestUtils.openNewBrowserWindow({
+        private: privateWin,
+      });
+      is(
+        win.gBrowser.currentURI.spec,
+        privateWin ? "about:privatebrowsing" : "about:blank",
+        "Expecting about:privatebrowsing or about:blank as URI of new window"
+      );
+
+      if (!privateWin) {
+        await waitForBookmarksToolbarVisibility({
+          win,
+          visible: visibilityState[1] == "always",
+          message:
+            "Toolbar should be visible only if visibilityState is 'always'. State: " +
+            visibilityState[1],
+        });
+        await BrowserTestUtils.openNewForegroundTab({
+          gBrowser: win.gBrowser,
+          opening: "about:newtab",
+          waitForLoad: false,
+        });
+      }
+
+      await waitForBookmarksToolbarVisibility({
+        win,
+        visible:
+          visibilityState[1] == "newtab" || visibilityState[1] == "always",
+        message:
+          "Toolbar should be visible as long as visibilityState isn't set to 'never'. State: " +
+          visibilityState[1],
+      });
+
+      await BrowserTestUtils.openNewForegroundTab({
+        gBrowser: win.gBrowser,
+        // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+        opening: "http://example.com",
+      });
+      await waitForBookmarksToolbarVisibility({
+        win,
+        visible: visibilityState[1] == "always",
+        message:
+          "Toolbar should be visible only if visibilityState is 'always'. State: " +
+          visibilityState[1],
+      });
+      await BrowserTestUtils.closeWindow(win);
+    }
+  }
+});
diff --git a/browser/base/content/test/about/browser_aboutStopReload.js b/browser/base/content/test/about/browser_aboutStopReload.js
new file mode 100644
index 0000000000..66c11a3de3
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutStopReload.js
@@ -0,0 +1,169 @@
+async function waitForNoAnimation(elt) {
+  return TestUtils.waitForCondition(() => !elt.hasAttribute("animate"));
+}
+
+async function getAnimatePromise(elt) {
+  return BrowserTestUtils.waitForAttribute("animate", elt).then(() =>
+    Assert.ok(true, `${elt.id} should animate`)
+  );
+}
+
+function stopReloadMutationCallback() {
+  Assert.ok(
+    false,
+    "stop-reload's animate attribute should not have been mutated"
+  );
+}
+
+// Force-enable the animation
+gReduceMotionOverride = false;
+
+add_task(async function checkDontShowStopOnNewTab() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+  let stopReloadContainerObserver = new MutationObserver(
+    stopReloadMutationCallback
+  );
+
+  await waitForNoAnimation(stopReloadContainer);
+  stopReloadContainerObserver.observe(stopReloadContainer, {
+    attributeFilter: ["animate"],
+  });
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:robots",
+    waitForStateStop: true,
+  });
+  BrowserTestUtils.removeTab(tab);
+
+  Assert.ok(
+    true,
+    "Test finished: stop-reload does not animate when navigating to local URI on new tab"
+  );
+  stopReloadContainerObserver.disconnect();
+});
+
+add_task(async function checkDontShowStopFromLocalURI() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+  let stopReloadContainerObserver = new MutationObserver(
+    stopReloadMutationCallback
+  );
+
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:robots",
+    waitForStateStop: true,
+  });
+  await waitForNoAnimation(stopReloadContainer);
+  stopReloadContainerObserver.observe(stopReloadContainer, {
+    attributeFilter: ["animate"],
+  });
+  BrowserTestUtils.loadURIString(tab.linkedBrowser, "about:mozilla");
+  BrowserTestUtils.removeTab(tab);
+
+  Assert.ok(
+    true,
+    "Test finished: stop-reload does not animate when navigating between local URIs"
+  );
+  stopReloadContainerObserver.disconnect();
+});
+
+add_task(async function checkDontShowStopFromNonLocalURI() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+  let stopReloadContainerObserver = new MutationObserver(
+    stopReloadMutationCallback
+  );
+
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "https://example.com",
+    waitForStateStop: true,
+  });
+  await waitForNoAnimation(stopReloadContainer);
+  stopReloadContainerObserver.observe(stopReloadContainer, {
+    attributeFilter: ["animate"],
+  });
+  BrowserTestUtils.loadURIString(tab.linkedBrowser, "about:mozilla");
+  BrowserTestUtils.removeTab(tab);
+
+  Assert.ok(
+    true,
+    "Test finished: stop-reload does not animate when navigating to local URI from non-local URI"
+  );
+  stopReloadContainerObserver.disconnect();
+});
+
+add_task(async function checkDoShowStopOnNewTab() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+  let reloadButton = document.getElementById("reload-button");
+  let stopPromise = BrowserTestUtils.waitForAttribute(
+    "displaystop",
+    reloadButton
+  );
+
+  await waitForNoAnimation(stopReloadContainer);
+
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "https://example.com",
+    waitForStateStop: true,
+  });
+  await stopPromise;
+  await waitForNoAnimation(stopReloadContainer);
+  BrowserTestUtils.removeTab(tab);
+
+  info(
+    "Test finished: stop-reload shows stop when navigating to non-local URI during tab opening"
+  );
+});
+
+add_task(async function checkAnimateStopOnTabAfterTabFinishesOpening() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+
+  await waitForNoAnimation(stopReloadContainer);
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    waitForStateStop: true,
+  });
+  await TestUtils.waitForCondition(() => {
+    info(
+      "Waiting for tabAnimationsInProgress to equal 0, currently " +
+        gBrowser.tabAnimationsInProgress
+    );
+    return !gBrowser.tabAnimationsInProgress;
+  });
+  let animatePromise = getAnimatePromise(stopReloadContainer);
+  BrowserTestUtils.loadURIString(tab.linkedBrowser, "https://example.com");
+  await animatePromise;
+  BrowserTestUtils.removeTab(tab);
+
+  info(
+    "Test finished: stop-reload animates when navigating to non-local URI on new tab after tab has opened"
+  );
+});
+
+add_task(async function checkDoShowStopFromLocalURI() {
+  let stopReloadContainer = document.getElementById("stop-reload-button");
+
+  await waitForNoAnimation(stopReloadContainer);
+  let tab = await BrowserTestUtils.openNewForegroundTab({
+    gBrowser,
+    opening: "about:robots",
+    waitForStateStop: true,
+  });
+  await TestUtils.waitForCondition(() => {
+    info(
+      "Waiting for tabAnimationsInProgress to equal 0, currently " +
+        gBrowser.tabAnimationsInProgress
+    );
+    return !gBrowser.tabAnimationsInProgress;
+  });
+  let animatePromise = getAnimatePromise(stopReloadContainer);
+  BrowserTestUtils.loadURIString(tab.linkedBrowser, "https://example.com");
+  await animatePromise;
+  await waitForNoAnimation(stopReloadContainer);
+  BrowserTestUtils.removeTab(tab);
+
+  info(
+    "Test finished: stop-reload animates when navigating to non-local URI from local URI"
+  );
+});
diff --git a/browser/base/content/test/about/browser_aboutSupport.js b/browser/base/content/test/about/browser_aboutSupport.js
new file mode 100644
index 0000000000..e846a2b493
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutSupport.js
@@ -0,0 +1,146 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const { ExperimentAPI } = ChromeUtils.importESModule(
+  "resource://nimbus/ExperimentAPI.sys.mjs"
+);
+const { ExperimentFakes } = ChromeUtils.importESModule(
+  "resource://testing-common/NimbusTestUtils.sys.mjs"
+);
+
+add_task(async function () {
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:support" },
+    async function (browser) {
+      let keyLocationServiceGoogleStatus = await SpecialPowers.spawn(
+        browser,
+        [],
+        async function () {
+          let textBox = content.document.getElementById(
+            "key-location-service-google-box"
+          );
+          await ContentTaskUtils.waitForCondition(
+            () => content.document.l10n.getAttributes(textBox).id,
+            "Google location service API key status loaded"
+          );
+          return content.document.l10n.getAttributes(textBox).id;
+        }
+      );
+      ok(
+        keyLocationServiceGoogleStatus,
+        "Google location service API key status shown"
+      );
+
+      let keySafebrowsingGoogleStatus = await SpecialPowers.spawn(
+        browser,
+        [],
+        async function () {
+          let textBox = content.document.getElementById(
+            "key-safebrowsing-google-box"
+          );
+          await ContentTaskUtils.waitForCondition(
+            () => content.document.l10n.getAttributes(textBox).id,
+            "Google Safebrowsing API key status loaded"
+          );
+          return content.document.l10n.getAttributes(textBox).id;
+        }
+      );
+      ok(
+        keySafebrowsingGoogleStatus,
+        "Google Safebrowsing API key status shown"
+      );
+
+      let keyMozillaStatus = await SpecialPowers.spawn(
+        browser,
+        [],
+        async function () {
+          let textBox = content.document.getElementById("key-mozilla-box");
+          await ContentTaskUtils.waitForCondition(
+            () => content.document.l10n.getAttributes(textBox).id,
+            "Mozilla API key status loaded"
+          );
+          return content.document.l10n.getAttributes(textBox).id;
+        }
+      );
+      ok(keyMozillaStatus, "Mozilla API key status shown");
+    }
+  );
+});
+
+add_task(async function test_nimbus_experiments() {
+  await ExperimentAPI.ready();
+  let doExperimentCleanup = await ExperimentFakes.enrollWithFeatureConfig({
+    featureId: "aboutwelcome",
+    value: { enabled: true },
+  });
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:support" },
+    async function (browser) {
+      let experimentName = await SpecialPowers.spawn(
+        browser,
+        [],
+        async function () {
+          await ContentTaskUtils.waitForCondition(
+            () =>
+              content.document.querySelector(
+                "#remote-experiments-tbody tr:first-child td"
+              )?.innerText
+          );
+          return content.document.querySelector(
+            "#remote-experiments-tbody tr:first-child td"
+          ).innerText;
+        }
+      );
+      ok(
+        experimentName.match("Nimbus"),
+        "Rendered the expected experiment slug"
+      );
+    }
+  );
+
+  await doExperimentCleanup();
+});
+
+add_task(async function test_remote_configuration() {
+  await ExperimentAPI.ready();
+  let doCleanup = await ExperimentFakes.enrollWithRollout({
+    featureId: NimbusFeatures.aboutwelcome.featureId,
+    value: { enabled: true },
+  });
+
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:support" },
+    async function (browser) {
+      let [userFacingName, branch] = await SpecialPowers.spawn(
+        browser,
+        [],
+        async function () {
+          await ContentTaskUtils.waitForCondition(
+            () =>
+              content.document.querySelector(
+                "#remote-features-tbody tr:first-child td"
+              )?.innerText
+          );
+          let rolloutName = content.document.querySelector(
+            "#remote-features-tbody tr:first-child td"
+          ).innerText;
+          let branchName = content.document.querySelector(
+            "#remote-features-tbody tr:first-child td:nth-child(2)"
+          ).innerText;
+
+          return [rolloutName, branchName];
+        }
+      );
+      ok(
+        userFacingName.match("NimbusTestUtils"),
+        "Rendered the expected rollout"
+      );
+      ok(branch.match("aboutwelcome"), "Rendered the expected rollout branch");
+    }
+  );
+
+  await doCleanup();
+});
diff --git a/browser/base/content/test/about/browser_aboutSupport_newtab_security_state.js b/browser/base/content/test/about/browser_aboutSupport_newtab_security_state.js
new file mode 100644
index 0000000000..caa45a1af5
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutSupport_newtab_security_state.js
@@ -0,0 +1,19 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+add_task(async function checkIdentityOfAboutSupport() {
+  let tab = gBrowser.addTab("about:support", {
+    referrerURI: null,
+    inBackground: false,
+    allowThirdPartyFixup: false,
+    relatedToCurrent: false,
+    skipAnimation: true,
+    allowMixedContent: false,
+    triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+  });
+
+  await promiseTabLoaded(tab);
+  let identityBox = document.getElementById("identity-box");
+  is(identityBox.className, "chromeUI", "Should know that we're chrome.");
+  gBrowser.removeTab(tab);
+});
diff --git a/browser/base/content/test/about/browser_aboutSupport_places.js b/browser/base/content/test/about/browser_aboutSupport_places.js
new file mode 100644
index 0000000000..e971de7f0e
--- /dev/null
+++ b/browser/base/content/test/about/browser_aboutSupport_places.js
@@ -0,0 +1,45 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function test_places_db_stats_table() {
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: "about:support" },
+    async function (browser) {
+      const [initialToggleText, toggleTextAfterShow, toggleTextAfterHide] =
+        await SpecialPowers.spawn(browser, [], async function () {
+          const toggleButton = content.document.getElementById(
+            "place-database-stats-toggle"
+          );
+          const getToggleText = () =>
+            content.document.l10n.getAttributes(toggleButton).id;
+          const toggleTexts = [];
+          const table = content.document.getElementById(
+            "place-database-stats-tbody"
+          );
+          await ContentTaskUtils.waitForCondition(
+            () => table.style.display === "none",
+            "Stats table is hidden initially"
+          );
+          toggleTexts.push(getToggleText());
+          toggleButton.click();
+          await ContentTaskUtils.waitForCondition(
+            () => table.style.display === "",
+            "Stats table is shown after first toggle"
+          );
+          toggleTexts.push(getToggleText());
+          toggleButton.click();
+          await ContentTaskUtils.waitForCondition(
+            () => table.style.display === "none",
+            "Stats table is hidden after second toggle"
+          );
+          toggleTexts.push(getToggleText());
+          return toggleTexts;
+        });
+      Assert.equal(initialToggleText, "place-database-stats-show");
+      Assert.equal(toggleTextAfterShow, "place-database-stats-hide");
+      Assert.equal(toggleTextAfterHide, "place-database-stats-show");
+    }
+  );
+});
diff --git a/browser/base/content/test/about/browser_bug435325.js b/browser/base/content/test/about/browser_bug435325.js
new file mode 100644
index 0000000000..70a3b272a9
--- /dev/null
+++ b/browser/base/content/test/about/browser_bug435325.js
@@ -0,0 +1,58 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/* Ensure that clicking the button in the Offline mode neterror page makes the browser go online. See bug 435325. */
+
+add_task(async function checkSwitchPageToOnlineMode() {
+  // Go offline and disable the proxy and cache, then try to load the test URL.
+  Services.io.offline = true;
+
+  // Tests always connect to localhost, and per bug 87717, localhost is now
+  // reachable in offline mode.  To avoid this, disable any proxy.
+  let proxyPrefValue = SpecialPowers.getIntPref("network.proxy.type");
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["network.proxy.type", 0],
+      ["browser.cache.disk.enable", false],
+      ["browser.cache.memory.enable", false],
+    ],
+  });
+
+  await BrowserTestUtils.withNewTab("about:blank", async function (browser) {
+    let netErrorLoaded = BrowserTestUtils.waitForErrorPage(browser);
+
+    // eslint-disable-next-line @microsoft/sdl/no-insecure-url
+    BrowserTestUtils.loadURIString(browser, "http://example.com/");
+    await netErrorLoaded;
+
+    // Re-enable the proxy so example.com is resolved to localhost, rather than
+    // the actual example.com.
+    await SpecialPowers.pushPrefEnv({
+      set: [["network.proxy.type", proxyPrefValue]],
+    });
+    let changeObserved = TestUtils.topicObserved(
+      "network:offline-status-changed"
+    );
+
+    // Click on the 'Try again' button.
+    await SpecialPowers.spawn(browser, [], async function () {
+      ok(
+        content.document.documentURI.startsWith("about:neterror?e=netOffline"),
+        "Should be showing error page"
+      );
+      content.document
+        .querySelector("#netErrorButtonContainer > .try-again")
+        .click();
+    });
+
+    await changeObserved;
+    ok(
+      !Services.io.offline,
+      "After clicking the 'Try Again' button, we're back online."
+    );
+  });
+});
+
+registerCleanupFunction(function () {
+  Services.io.offline = false;
+});
diff --git a/browser/base/content/test/about/browser_bug633691.js b/browser/base/content/test/about/browser_bug633691.js
new file mode 100644
index 0000000000..33d58475f6
--- /dev/null
+++ b/browser/base/content/test/about/browser_bug633691.js
@@ -0,0 +1,32 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+add_task(async function test() {
+  const URL = "data:text/html,<iframe width='700' height='700'></iframe>";
+  await BrowserTestUtils.withNewTab(
+    { gBrowser, url: URL },
+    async function (browser) {
+      let context = await SpecialPowers.spawn(browser, [], function () {
+        let iframe = content.document.querySelector("iframe");
+        iframe.src = "https://expired.example.com/";
+        return BrowsingContext.getFromWindow(iframe.contentWindow);
+      });
+      await TestUtils.waitForCondition(() => {
+        let frame = context.currentWindowGlobal;
+        return frame && frame.documentURI.spec.startsWith("about:certerror");
+      });
+      await SpecialPowers.spawn(context, [], async function () {
+        await ContentTaskUtils.waitForCondition(
+          () => content.document.readyState == "interactive"
+        );
+        let aP = content.document.getElementById("badCertAdvancedPanel");
+        Assert.ok(aP, "Advanced content should exist");
+        Assert.ok(
+          ContentTaskUtils.is_hidden(aP),
+          "Advanced content should not be visible by default"
+        );
+      });
+    }
+  );
+});
diff --git a/browser/base/content/test/about/csp_iframe.sjs b/browser/base/content/test/about/csp_iframe.sjs
new file mode 100644
index 0000000000..f53ed8498f
--- /dev/null
+++ b/browser/base/content/test/about/csp_iframe.sjs
@@ -0,0 +1,33 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function handleRequest(request, response) {
+  // let's enjoy the amazing CSP setting
+  response.setHeader(
+    "Content-Security-Policy",
+    "frame-ancestors 'self'",
+    false
+  );
+
+  // let's avoid caching issues
+  response.setHeader("Pragma", "no-cache");
+  response.setHeader("Cache-Control", "no-cache", false);
+
+  // everything is fine - no needs to worry :)
+  response.setStatusLine(request.httpVersion, 200);
+  response.setHeader("Content-Type", "text/html", false);
+  let txt = "<html><body><h1>CSP Page opened in new window!</h1></body></html>";
+  response.write(txt);
+
+  let cookie = request.hasHeader("Cookie")
+    ? request.getHeader("Cookie")
+    : "<html><body>" +
+      "<h2 id='strictCookie'>No same site strict cookie header</h2>" +
+      "</body></html>";
+  response.write(cookie);
+
+  if (!request.hasHeader("Cookie")) {
+    let strictCookie = `matchaCookie=green; Domain=.example.org; SameSite=Strict`;
+    response.setHeader("Set-Cookie", strictCookie);
+  }
+}
diff --git a/browser/base/content/test/about/dummy_page.html b/browser/base/content/test/about/dummy_page.html
new file mode 100644
index 0000000000..1a87e28408
--- /dev/null
+++ b/browser/base/content/test/about/dummy_page.html
@@ -0,0 +1,9 @@
+<html>
+<head>
+<title>Dummy test page</title>
+<meta http-equiv="Content-Type" content="text/html;charset=utf-8"></meta>
+</head>
+<body>
+<p>Dummy test page</p>
+</body>
+</html>
diff --git a/browser/base/content/test/about/head.js b/browser/base/content/test/about/head.js
new file mode 100644
index 0000000000..c723fbee33
--- /dev/null
+++ b/browser/base/content/test/about/head.js
@@ -0,0 +1,220 @@
+ChromeUtils.defineESModuleGetters(this, {
+  FormHistory: "resource://gre/modules/FormHistory.sys.mjs",
+  SearchTestUtils: "resource://testing-common/SearchTestUtils.sys.mjs",
+});
+
+SearchTestUtils.init(this);
+
+function getCertChainAsString(certBase64Array) {
+  let certChain = "";
+  for (let cert of certBase64Array) {
+    certChain += getPEMString(cert);
+  }
+  return certChain;
+}
+
+function getPEMString(derb64) {
+  // Wrap the Base64 string into lines of 64 characters,
+  // with CRLF line breaks (as specified in RFC 1421).
+  var wrapped = derb64.replace(/(\S{64}(?!$))/g, "$1\r\n");
+  return (
+    "-----BEGIN CERTIFICATE-----\r\n" +
+    wrapped +
+    "\r\n-----END CERTIFICATE-----\r\n"
+  );
+}
+
+async function injectErrorPageFrame(tab, src, sandboxed) {
+  let loadedPromise = BrowserTestUtils.browserLoaded(
+    tab.linkedBrowser,
+    true,
+    null,
+    true
+  );
+
+  await SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [src, sandboxed],
+    async function (frameSrc, frameSandboxed) {
+      let iframe = content.document.createElement("iframe");
+      iframe.src = frameSrc;
+      if (frameSandboxed) {
+        iframe.setAttribute("sandbox", "allow-scripts");
+      }
+      content.document.body.appendChild(iframe);
+    }
+  );
+
+  await loadedPromise;
+}
+
+async function openErrorPage(src, useFrame, sandboxed) {
+  let dummyPage =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      "https://example.com"
+    ) + "dummy_page.html";
+
+  let tab;
+  if (useFrame) {
+    info("Loading cert error page in an iframe");
+    tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, dummyPage);
+    await injectErrorPageFrame(tab, src, sandboxed);
+  } else {
+    let certErrorLoaded;
+    tab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      () => {
+        gBrowser.selectedTab = BrowserTestUtils.addTab(gBrowser, src);
+        let browser = gBrowser.selectedBrowser;
+        certErrorLoaded = BrowserTestUtils.waitForErrorPage(browser);
+      },
+      false
+    );
+    info("Loading and waiting for the cert error");
+    await certErrorLoaded;
+  }
+
+  return tab;
+}
+
+function waitForCondition(condition, nextTest, errorMsg, retryTimes) {
+  retryTimes = typeof retryTimes !== "undefined" ? retryTimes : 30;
+  var tries = 0;
+  var interval = setInterval(function () {
+    if (tries >= retryTimes) {
+      ok(false, errorMsg);
+      moveOn();
+    }
+    var conditionPassed;
+    try {
+      conditionPassed = condition();
+    } catch (e) {
+      ok(false, e + "\n" + e.stack);
+      conditionPassed = false;
+    }
+    if (conditionPassed) {
+      moveOn();
+    }
+    tries++;
+  }, 100);
+  var moveOn = function () {
+    clearInterval(interval);
+    nextTest();
+  };
+}
+
+function whenTabLoaded(aTab, aCallback) {
+  promiseTabLoadEvent(aTab).then(aCallback);
+}
+
+function promiseTabLoaded(aTab) {
+  return new Promise(resolve => {
+    whenTabLoaded(aTab, resolve);
+  });
+}
+
+/**
+ * Waits for a load (or custom) event to finish in a given tab. If provided
+ * load an uri into the tab.
+ *
+ * @param tab
+ *        The tab to load into.
+ * @param [optional] url
+ *        The url to load, or the current url.
+ * @return {Promise} resolved when the event is handled.
+ * @resolves to the received event
+ * @rejects if a valid load event is not received within a meaningful interval
+ */
+function promiseTabLoadEvent(tab, url) {
+  info("Wait tab event: load");
+
+  function handle(loadedUrl) {
+    if (loadedUrl === "about:blank" || (url && loadedUrl !== url)) {
+      info(`Skipping spurious load event for ${loadedUrl}`);
+      return false;
+    }
+
+    info("Tab event received: load");
+    return true;
+  }
+
+  let loaded = BrowserTestUtils.browserLoaded(tab.linkedBrowser, false, handle);
+
+  if (url) {
+    BrowserTestUtils.loadURIString(tab.linkedBrowser, url);
+  }
+
+  return loaded;
+}
+
+/**
+ * Wait for the search engine to change. searchEngineChangeFn is a function
+ * that will be called to change the search engine.
+ */
+async function promiseContentSearchChange(browser, searchEngineChangeFn) {
+  // Add an event listener manually then perform the action, rather than using
+  // BrowserTestUtils.addContentEventListener as that doesn't add the listener
+  // early enough.
+  await SpecialPowers.spawn(browser, [], async () => {
+    // Store the results in a temporary place.
+    content._searchDetails = {
+      defaultEnginesList: [],
+      listener: event => {
+        if (event.detail.type == "CurrentState") {
+          content._searchDetails.defaultEnginesList.push(
+            content.wrappedJSObject.gContentSearchController.defaultEngine.name
+          );
+        }
+      },
+    };
+
+    // Listen using the system group to ensure that it fires after
+    // the default behaviour.
+    content.addEventListener(
+      "ContentSearchService",
+      content._searchDetails.listener,
+      { mozSystemGroup: true }
+    );
+  });
+
+  let expectedEngineName = await searchEngineChangeFn();
+
+  await SpecialPowers.spawn(
+    browser,
+    [expectedEngineName],
+    async expectedEngineNameChild => {
+      await ContentTaskUtils.waitForCondition(
+        () =>
+          content._searchDetails.defaultEnginesList &&
+          content._searchDetails.defaultEnginesList[
+            content._searchDetails.defaultEnginesList.length - 1
+          ] == expectedEngineNameChild
+      );
+      content.removeEventListener(
+        "ContentSearchService",
+        content._searchDetails.listener,
+        { mozSystemGroup: true }
+      );
+      delete content._searchDetails;
+    }
+  );
+}
+
+async function waitForBookmarksToolbarVisibility({
+  win = window,
+  visible,
+  message,
+}) {
+  let result = await TestUtils.waitForCondition(() => {
+    let toolbar = win.document.getElementById("PersonalToolbar");
+    return toolbar && (visible ? !toolbar.collapsed : toolbar.collapsed);
+  }, message || "waiting for toolbar to become " + (visible ? "visible" : "hidden"));
+  ok(result, message);
+  return result;
+}
+
+function isBookmarksToolbarVisible(win = window) {
+  let toolbar = win.document.getElementById("PersonalToolbar");
+  return !toolbar.collapsed;
+}
diff --git a/browser/base/content/test/about/iframe_page_csp.html b/browser/base/content/test/about/iframe_page_csp.html
new file mode 100644
index 0000000000..93a23de15d
--- /dev/null
+++ b/browser/base/content/test/about/iframe_page_csp.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>Dummy iFrame page</title>
+</head>
+<body>
+<h1>iFrame CSP test</h1>
+<iframe id="theIframe"
+        sandbox="allow-scripts"
+        width=800
+        height=800
+        src="http://example.org:8000/browser/browser/base/content/test/about/csp_iframe.sjs">
+</iframe>
+</body>
+</html>
diff --git a/browser/base/content/test/about/iframe_page_xfo.html b/browser/base/content/test/about/iframe_page_xfo.html
new file mode 100644
index 0000000000..34e7f5cc52
--- /dev/null
+++ b/browser/base/content/test/about/iframe_page_xfo.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>Dummy iFrame page</title>
+</head>
+<body>
+<h1>iFrame XFO test</h1>
+<iframe id="theIframe"
+        sandbox="allow-scripts"
+        width=800
+        height=800
+        src="http://example.org:8000/browser/browser/base/content/test/about/xfo_iframe.sjs">
+</iframe>
+</body>
+</html>
diff --git a/browser/base/content/test/about/print_postdata.sjs b/browser/base/content/test/about/print_postdata.sjs
new file mode 100644
index 0000000000..0e3ef38419
--- /dev/null
+++ b/browser/base/content/test/about/print_postdata.sjs
@@ -0,0 +1,25 @@
+const CC = Components.Constructor;
+const BinaryInputStream = CC(
+  "@mozilla.org/binaryinputstream;1",
+  "nsIBinaryInputStream",
+  "setInputStream"
+);
+
+function handleRequest(request, response) {
+  response.setHeader("Content-Type", "text/plain", false);
+  if (request.method == "GET") {
+    response.write(request.queryString);
+  } else {
+    var body = new BinaryInputStream(request.bodyInputStream);
+
+    var avail;
+    var bytes = [];
+
+    while ((avail = body.available()) > 0) {
+      Array.prototype.push.apply(bytes, body.readByteArray(avail));
+    }
+
+    var data = String.fromCharCode.apply(null, bytes);
+    response.bodyOutputStream.write(data, data.length);
+  }
+}
diff --git a/browser/base/content/test/about/searchSuggestionEngine.sjs b/browser/base/content/test/about/searchSuggestionEngine.sjs
new file mode 100644
index 0000000000..1978b4f665
--- /dev/null
+++ b/browser/base/content/test/about/searchSuggestionEngine.sjs
@@ -0,0 +1,9 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function handleRequest(req, resp) {
+  let suffixes = ["foo", "bar"];
+  let data = [req.queryString, suffixes.map(s => req.queryString + s)];
+  resp.setHeader("Content-Type", "application/json", false);
+  resp.write(JSON.stringify(data));
+}
diff --git a/browser/base/content/test/about/searchSuggestionEngine.xml b/browser/base/content/test/about/searchSuggestionEngine.xml
new file mode 100644
index 0000000000..409d0b4084
--- /dev/null
+++ b/browser/base/content/test/about/searchSuggestionEngine.xml
@@ -0,0 +1,11 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+
+<SearchPlugin xmlns="http://www.mozilla.org/2006/browser/search/">
+<ShortName>browser_searchSuggestionEngine searchSuggestionEngine.xml</ShortName>
+<Url type="application/x-suggestions+json" method="GET" template="http://mochi.test:8888/browser/browser/base/content/test/about/searchSuggestionEngine.sjs?{searchTerms}"/>
+<Url type="text/html" method="GET" template="http://mochi.test:8888/" rel="searchform">
+  <Param name="terms" value="{searchTerms}"/>
+</Url>
+</SearchPlugin>
diff --git a/browser/base/content/test/about/slow_loading_page.sjs b/browser/base/content/test/about/slow_loading_page.sjs
new file mode 100644
index 0000000000..747390cdf7
--- /dev/null
+++ b/browser/base/content/test/about/slow_loading_page.sjs
@@ -0,0 +1,29 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const DELAY_MS = 400;
+
+const HTML = `<!DOCTYPE HTML>
+<html dir="ltr" xml:lang="en-US" lang="en-US">
+  <head>
+    <meta charset="utf8">
+  </head>
+  <body>hi mom!
+  </body>
+</html>`;
+
+function handleRequest(req, resp) {
+  resp.processAsync();
+
+  let timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
+  timer.init(
+    () => {
+      resp.setHeader("Cache-Control", "no-cache", false);
+      resp.setHeader("Content-Type", "text/html;charset=utf-8", false);
+      resp.write(HTML);
+      resp.finish();
+    },
+    DELAY_MS,
+    Ci.nsITimer.TYPE_ONE_SHOT
+  );
+}
diff --git a/browser/base/content/test/about/xfo_iframe.sjs b/browser/base/content/test/about/xfo_iframe.sjs
new file mode 100644
index 0000000000..e8a6352ce0
--- /dev/null
+++ b/browser/base/content/test/about/xfo_iframe.sjs
@@ -0,0 +1,34 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+function handleRequest(request, response) {
+  // let's enjoy the amazing XFO setting
+  response.setHeader("X-Frame-Options", "SAMEORIGIN");
+
+  // let's avoid caching issues
+  response.setHeader("Pragma", "no-cache");
+  response.setHeader("Cache-Control", "no-cache", false);
+
+  // everything is fine - no needs to worry :)
+  response.setStatusLine(request.httpVersion, 200);
+
+  response.setHeader("Content-Type", "text/html", false);
+  let txt =
+    "<html><head><title>XFO page</title></head>" +
+    "<body><h1>" +
+    "XFO blocked page opened in new window!" +
+    "</h1></body></html>";
+  response.write(txt);
+
+  let cookie = request.hasHeader("Cookie")
+    ? request.getHeader("Cookie")
+    : "<html><body>" +
+      "<h2 id='strictCookie'>No same site strict cookie header</h2></body>" +
+      "</html>";
+  response.write(cookie);
+
+  if (!request.hasHeader("Cookie")) {
+    let strictCookie = `matchaCookie=creamy; Domain=.example.org; SameSite=Strict`;
+    response.setHeader("Set-Cookie", strictCookie);
+  }
+}