Adding upstream version 86.0.1.upstream/86.0.1upstream

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

68 files changed, 6315 insertions, 0 deletions

diff --git a/uriloader/exthandler/tests/HandlerServiceTestUtils.jsm b/uriloader/exthandler/tests/HandlerServiceTestUtils.jsm
new file mode 100644
index 0000000000..72c551d654
--- /dev/null
+++ b/uriloader/exthandler/tests/HandlerServiceTestUtils.jsm
@@ -0,0 +1,241 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/*
+ * Shared functions for tests related to invoking external handler applications.
+ */
+
+"use strict";
+
+var EXPORTED_SYMBOLS = ["HandlerServiceTestUtils"];
+
+const { AppConstants } = ChromeUtils.import(
+  "resource://gre/modules/AppConstants.jsm"
+);
+const { XPCOMUtils } = ChromeUtils.import(
+  "resource://gre/modules/XPCOMUtils.jsm"
+);
+const { Assert } = ChromeUtils.import("resource://testing-common/Assert.jsm");
+
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gExternalProtocolService",
+  "@mozilla.org/uriloader/external-protocol-service;1",
+  "nsIExternalProtocolService"
+);
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gMIMEService",
+  "@mozilla.org/mime;1",
+  "nsIMIMEService"
+);
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gHandlerService",
+  "@mozilla.org/uriloader/handler-service;1",
+  "nsIHandlerService"
+);
+
+var HandlerServiceTestUtils = {
+  /**
+   * Retrieves the names of all the MIME types and protocols configured in the
+   * handler service instance currently under testing.
+   *
+   * @return Array of strings like "example/type" or "example-scheme", sorted
+   *         alphabetically regardless of category.
+   */
+  getAllHandlerInfoTypes() {
+    return Array.from(gHandlerService.enumerate(), info => info.type).sort();
+  },
+
+  /**
+   * Retrieves all the configured handlers for MIME types and protocols.
+   *
+   * @note The nsIHandlerInfo instances returned by the "enumerate" method
+   *       cannot be used for testing because they incorporate information from
+   *       the operating system and also from the default nsIHandlerService
+   *       instance, independently from what instance is under testing.
+   *
+   * @return Array of nsIHandlerInfo instances sorted by their "type" property.
+   */
+  getAllHandlerInfos() {
+    return this.getAllHandlerInfoTypes().map(type => this.getHandlerInfo(type));
+  },
+
+  /**
+   * Retrieves an nsIHandlerInfo for the given MIME type or protocol, which
+   * incorporates information from the operating system and also from the
+   * handler service instance currently under testing.
+   *
+   * @note If the handler service instance currently under testing is not the
+   *       default one and the requested type is a MIME type, the returned
+   *       nsIHandlerInfo will include information from the default
+   *       nsIHandlerService instance. This cannot be avoided easily because the
+   *       getMIMEInfoFromOS method is not exposed to JavaScript.
+   *
+   * @param type
+   *        MIME type or scheme name of the nsIHandlerInfo to retrieve.
+   *
+   * @return The populated nsIHandlerInfo instance.
+   */
+  getHandlerInfo(type) {
+    if (type.includes("/")) {
+      // We have to use the getFromTypeAndExtension method because we don't have
+      // access to getMIMEInfoFromOS. This means that we have to reset the data
+      // that may have been imported from the default nsIHandlerService instance
+      // and is not overwritten by fillHandlerInfo later.
+      let handlerInfo = gMIMEService.getFromTypeAndExtension(type, null);
+      if (AppConstants.platform == "android") {
+        // On Android, the first handler application is always the internal one.
+        while (handlerInfo.possibleApplicationHandlers.length > 1) {
+          handlerInfo.possibleApplicationHandlers.removeElementAt(1);
+        }
+      } else {
+        handlerInfo.possibleApplicationHandlers.clear();
+      }
+      handlerInfo.setFileExtensions("");
+      // Populate the object from the handler service instance under testing.
+      if (gHandlerService.exists(handlerInfo)) {
+        gHandlerService.fillHandlerInfo(handlerInfo, "");
+      }
+      return handlerInfo;
+    }
+
+    // Populate the protocol information from the handler service instance under
+    // testing, like the nsIExternalProtocolService::GetProtocolHandlerInfo
+    // method does on the default nsIHandlerService instance.
+    let osDefaultHandlerFound = {};
+    let handlerInfo = gExternalProtocolService.getProtocolHandlerInfoFromOS(
+      type,
+      osDefaultHandlerFound
+    );
+    if (gHandlerService.exists(handlerInfo)) {
+      gHandlerService.fillHandlerInfo(handlerInfo, "");
+    } else {
+      gExternalProtocolService.setProtocolHandlerDefaults(
+        handlerInfo,
+        osDefaultHandlerFound.value
+      );
+    }
+    return handlerInfo;
+  },
+
+  /**
+   * Creates an nsIHandlerInfo for the given MIME type or protocol, initialized
+   * to the default values for the current platform.
+   *
+   * @note For this method to work, the specified MIME type or protocol must not
+   *       be configured in the default handler service instance or the one
+   *       under testing, and must not be registered in the operating system.
+   *
+   * @param type
+   *        MIME type or scheme name of the nsIHandlerInfo to create.
+   *
+   * @return The blank nsIHandlerInfo instance.
+   */
+  getBlankHandlerInfo(type) {
+    let handlerInfo = this.getHandlerInfo(type);
+
+    let preferredAction, preferredApplicationHandler;
+    if (AppConstants.platform == "android") {
+      // On Android, the default preferredAction for MIME types is useHelperApp.
+      // For protocols, we always behave as if an operating system provided
+      // handler existed, and as such we initialize them to useSystemDefault.
+      // This is because the AndroidBridge is not available in xpcshell tests.
+      preferredAction = type.includes("/")
+        ? Ci.nsIHandlerInfo.useHelperApp
+        : Ci.nsIHandlerInfo.useSystemDefault;
+      // On Android, the default handler application is always the internal one.
+      preferredApplicationHandler = {
+        name: "Android chooser",
+      };
+    } else {
+      // On Desktop, the default preferredAction for MIME types is saveToDisk,
+      // while for protocols it is alwaysAsk.
+      preferredAction = type.includes("/")
+        ? Ci.nsIHandlerInfo.saveToDisk
+        : Ci.nsIHandlerInfo.alwaysAsk;
+      preferredApplicationHandler = null;
+    }
+
+    this.assertHandlerInfoMatches(handlerInfo, {
+      type,
+      preferredAction,
+      alwaysAskBeforeHandling: true,
+      preferredApplicationHandler,
+    });
+    return handlerInfo;
+  },
+
+  /**
+   * Checks whether an nsIHandlerInfo instance matches the provided object.
+   */
+  assertHandlerInfoMatches(handlerInfo, expected) {
+    let expectedInterface = expected.type.includes("/")
+      ? Ci.nsIMIMEInfo
+      : Ci.nsIHandlerInfo;
+    Assert.ok(handlerInfo instanceof expectedInterface);
+    Assert.equal(handlerInfo.type, expected.type);
+
+    if (!expected.preferredActionOSDependent) {
+      Assert.equal(handlerInfo.preferredAction, expected.preferredAction);
+      Assert.equal(
+        handlerInfo.alwaysAskBeforeHandling,
+        expected.alwaysAskBeforeHandling
+      );
+    }
+
+    if (expectedInterface == Ci.nsIMIMEInfo) {
+      let fileExtensionsEnumerator = handlerInfo.getFileExtensions();
+      for (let expectedFileExtension of expected.fileExtensions || []) {
+        Assert.equal(fileExtensionsEnumerator.getNext(), expectedFileExtension);
+      }
+      Assert.ok(!fileExtensionsEnumerator.hasMore());
+    }
+
+    if (expected.preferredApplicationHandler) {
+      this.assertHandlerAppMatches(
+        handlerInfo.preferredApplicationHandler,
+        expected.preferredApplicationHandler
+      );
+    } else {
+      Assert.equal(handlerInfo.preferredApplicationHandler, null);
+    }
+
+    let handlerAppsArrayEnumerator = handlerInfo.possibleApplicationHandlers.enumerate();
+    if (AppConstants.platform == "android") {
+      // On Android, the first handler application is always the internal one.
+      this.assertHandlerAppMatches(handlerAppsArrayEnumerator.getNext(), {
+        name: "Android chooser",
+      });
+    }
+    for (let expectedHandlerApp of expected.possibleApplicationHandlers || []) {
+      this.assertHandlerAppMatches(
+        handlerAppsArrayEnumerator.getNext(),
+        expectedHandlerApp
+      );
+    }
+    Assert.ok(!handlerAppsArrayEnumerator.hasMoreElements());
+  },
+
+  /**
+   * Checks whether an nsIHandlerApp instance matches the provided object.
+   */
+  assertHandlerAppMatches(handlerApp, expected) {
+    Assert.ok(handlerApp instanceof Ci.nsIHandlerApp);
+    Assert.equal(handlerApp.name, expected.name);
+    if (expected.executable) {
+      Assert.ok(handlerApp instanceof Ci.nsILocalHandlerApp);
+      Assert.ok(expected.executable.equals(handlerApp.executable));
+    } else if (expected.uriTemplate) {
+      Assert.ok(handlerApp instanceof Ci.nsIWebHandlerApp);
+      Assert.equal(handlerApp.uriTemplate, expected.uriTemplate);
+    } else if (expected.service) {
+      Assert.ok(handlerApp instanceof Ci.nsIDBusHandlerApp);
+      Assert.equal(handlerApp.service, expected.service);
+      Assert.equal(handlerApp.method, expected.method);
+      Assert.equal(handlerApp.dBusInterface, expected.dBusInterface);
+      Assert.equal(handlerApp.objectPath, expected.objectPath);
+    }
+  },
+};
diff --git a/uriloader/exthandler/tests/WriteArgument.cpp b/uriloader/exthandler/tests/WriteArgument.cpp
new file mode 100644
index 0000000000..603965150e
--- /dev/null
+++ b/uriloader/exthandler/tests/WriteArgument.cpp
@@ -0,0 +1,20 @@
+#include <stdio.h>
+#include "prenv.h"
+
+int main(int argc, char* argv[]) {
+  if (argc != 2) return 1;
+
+  const char* value = PR_GetEnv("WRITE_ARGUMENT_FILE");
+
+  if (!value) return 2;
+
+  FILE* outfile = fopen(value, "w");
+  if (!outfile) return 3;
+
+  // We only need to write out the first argument (no newline).
+  fputs(argv[argc - 1], outfile);
+
+  fclose(outfile);
+
+  return 0;
+}
diff --git a/uriloader/exthandler/tests/mochitest/.eslintrc.js b/uriloader/exthandler/tests/mochitest/.eslintrc.js
new file mode 100644
index 0000000000..7612459de1
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = {
+  extends: ["plugin:mozilla/browser-test", "plugin:mozilla/mochitest-test"],
+};
diff --git a/uriloader/exthandler/tests/mochitest/HelperAppLauncherDialog_chromeScript.js b/uriloader/exthandler/tests/mochitest/HelperAppLauncherDialog_chromeScript.js
new file mode 100644
index 0000000000..d08d72b048
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/HelperAppLauncherDialog_chromeScript.js
@@ -0,0 +1,38 @@
+const { ComponentUtils } = ChromeUtils.import(
+  "resource://gre/modules/ComponentUtils.jsm"
+);
+
+const HELPERAPP_DIALOG_CONTRACT = "@mozilla.org/helperapplauncherdialog;1";
+const HELPERAPP_DIALOG_CID = Components.ID(
+  Cc[HELPERAPP_DIALOG_CONTRACT].number
+);
+
+const FAKE_CID = Cc["@mozilla.org/uuid-generator;1"]
+  .getService(Ci.nsIUUIDGenerator)
+  .generateUUID();
+/* eslint-env mozilla/frame-script */
+function HelperAppLauncherDialog() {}
+HelperAppLauncherDialog.prototype = {
+  show(aLauncher, aWindowContext, aReason) {
+    sendAsyncMessage("suggestedFileName", aLauncher.suggestedFileName);
+  },
+  QueryInterface: ChromeUtils.generateQI(["nsIHelperAppLauncherDialog"]),
+};
+
+var registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
+registrar.registerFactory(
+  FAKE_CID,
+  "",
+  HELPERAPP_DIALOG_CONTRACT,
+  ComponentUtils._getFactory(HelperAppLauncherDialog)
+);
+
+addMessageListener("unregister", function() {
+  registrar.registerFactory(
+    HELPERAPP_DIALOG_CID,
+    "",
+    HELPERAPP_DIALOG_CONTRACT,
+    null
+  );
+  sendAsyncMessage("unregistered");
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser.ini b/uriloader/exthandler/tests/mochitest/browser.ini
new file mode 100644
index 0000000000..0d5b20bef8
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser.ini
@@ -0,0 +1,51 @@
+[DEFAULT]
+head = head.js
+support-files =
+  protocolHandler.html
+
+[browser_auto_close_window.js]
+run-if = e10s # test relies on e10s behavior
+support-files =
+  download_page.html
+  download.bin
+  download.sjs
+[browser_download_always_ask_preferred_app.js]
+[browser_download_privatebrowsing.js]
+[browser_download_open_with_internal_handler.js]
+support-files =
+  file_pdf_application_pdf.pdf
+  file_pdf_application_pdf.pdf^headers^
+  file_pdf_application_unknown.pdf
+  file_pdf_application_unknown.pdf^headers^
+  file_pdf_binary_octet_stream.pdf
+  file_pdf_binary_octet_stream.pdf^headers^
+  file_txt_attachment_test.txt
+  file_txt_attachment_test.txt^headers^
+  file_xml_attachment_binary_octet_stream.xml
+  file_xml_attachment_binary_octet_stream.xml^headers^
+  file_xml_attachment_test.xml
+  file_xml_attachment_test.xml^headers^
+[browser_download_urlescape.js]
+support-files =
+  file_with@@funny_name.png
+  file_with@@funny_name.png^headers^
+  file_with[funny_name.webm
+  file_with[funny_name.webm^headers^
+[browser_extension_correction.js]
+support-files =
+  file_as.exe
+  file_as.exe^headers^
+[browser_open_internal_choice_persistence.js]
+support-files =
+  file_pdf_application_pdf.pdf
+  file_pdf_application_pdf.pdf^headers^
+[browser_protocol_ask_dialog.js]
+support-files =
+  file_nested_protocol_request.html
+[browser_first_prompt_not_blocked_without_user_interaction.js]
+support-files =
+  file_external_protocol_iframe.html
+[browser_protocol_ask_dialog_permission.js]
+[browser_protocolhandler_loop.js]
+[browser_remember_download_option.js]
+[browser_web_protocol_handlers.js]
diff --git a/uriloader/exthandler/tests/mochitest/browser_auto_close_window.js b/uriloader/exthandler/tests/mochitest/browser_auto_close_window.js
new file mode 100644
index 0000000000..2e1d17e139
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_auto_close_window.js
@@ -0,0 +1,271 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { ComponentUtils } = ChromeUtils.import(
+  "resource://gre/modules/ComponentUtils.jsm"
+);
+
+const ROOT = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+const PAGE_URL = ROOT + "download_page.html";
+const SJS_URL = ROOT + "download.sjs";
+
+const HELPERAPP_DIALOG_CONTRACT_ID = "@mozilla.org/helperapplauncherdialog;1";
+const HELPERAPP_DIALOG_CID = Components.ID(
+  Cc[HELPERAPP_DIALOG_CONTRACT_ID].number
+);
+const MOCK_HELPERAPP_DIALOG_CID = Components.ID(
+  "{2f372b6f-56c9-46d5-af0d-9f09bb69860c}"
+);
+
+let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
+let curDialogResolve = null;
+
+function HelperAppLauncherDialog() {}
+
+HelperAppLauncherDialog.prototype = {
+  show(aLauncher, aWindowContext, aReason) {
+    ok(true, "Showing the helper app dialog");
+    curDialogResolve(aWindowContext);
+    executeSoon(() => {
+      aLauncher.cancel(Cr.NS_ERROR_ABORT);
+    });
+  },
+  QueryInterface: ChromeUtils.generateQI(["nsIHelperAppLauncherDialog"]),
+};
+
+function promiseHelperAppDialog() {
+  return new Promise(resolve => {
+    curDialogResolve = resolve;
+  });
+}
+
+let mockHelperAppService;
+
+add_task(async function setup() {
+  // Replace the real helper app dialog with our own.
+  mockHelperAppService = ComponentUtils._getFactory(HelperAppLauncherDialog);
+  registrar.registerFactory(
+    MOCK_HELPERAPP_DIALOG_CID,
+    "",
+    HELPERAPP_DIALOG_CONTRACT_ID,
+    mockHelperAppService
+  );
+});
+
+add_task(async function simple_navigation() {
+  // Tests that simple navigation gives us the right windowContext (that is,
+  // the window that we're using).
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    let dialogAppeared = promiseHelperAppDialog();
+    await BrowserTestUtils.synthesizeMouseAtCenter(
+      "#regular_load",
+      {},
+      browser
+    );
+    let windowContext = await dialogAppeared;
+
+    is(windowContext, browser.ownerGlobal, "got the right windowContext");
+  });
+});
+
+// Given a browser pointing to download_page.html, clicks on the link that
+// opens with target="_blank" (i.e. a new tab) and ensures that we
+// automatically open and close that tab.
+async function testNewTab(browser) {
+  let dialogAppeared = promiseHelperAppDialog();
+  let tabOpened = BrowserTestUtils.waitForEvent(
+    gBrowser.tabContainer,
+    "TabOpen"
+  ).then(event => {
+    return [event.target, BrowserTestUtils.waitForTabClosing(event.target)];
+  });
+
+  await BrowserTestUtils.synthesizeMouseAtCenter("#target_blank", {}, browser);
+
+  let windowContext = await dialogAppeared;
+  is(windowContext, browser.ownerGlobal, "got the right windowContext");
+  let [tab, closingPromise] = await tabOpened;
+  await closingPromise;
+  is(tab.linkedBrowser, null, "tab was opened and closed");
+}
+
+add_task(async function target_blank() {
+  // Tests that a link with target=_blank opens a new tab and closes it,
+  // returning the window that we're using for navigation.
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    await testNewTab(browser);
+  });
+});
+
+add_task(async function target_blank_no_opener() {
+  // Tests that a link with target=_blank and no opener opens a new tab
+  // and closes it, returning the window that we're using for navigation.
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let tabOpened = BrowserTestUtils.waitForEvent(
+      gBrowser.tabContainer,
+      "TabOpen"
+    ).then(event => {
+      return [event.target, BrowserTestUtils.waitForTabClosing(event.target)];
+    });
+
+    await BrowserTestUtils.synthesizeMouseAtCenter(
+      "#target_blank_no_opener",
+      {},
+      browser
+    );
+
+    let windowContext = await dialogAppeared;
+    is(windowContext, browser.ownerGlobal, "got the right windowContext");
+    let [tab, closingPromise] = await tabOpened;
+    await closingPromise;
+    is(tab.linkedBrowser, null, "tab was opened and closed");
+  });
+});
+
+add_task(async function open_in_new_tab_no_opener() {
+  // Tests that a link with target=_blank and no opener opens a new tab
+  // and closes it, returning the window that we're using for navigation.
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let tabOpened = BrowserTestUtils.waitForEvent(
+      gBrowser.tabContainer,
+      "TabOpen"
+    ).then(event => {
+      return [event.target, BrowserTestUtils.waitForTabClosing(event.target)];
+    });
+
+    await BrowserTestUtils.synthesizeMouseAtCenter(
+      "#open_in_new_tab_no_opener",
+      {},
+      browser
+    );
+
+    let windowContext = await dialogAppeared;
+    is(windowContext, browser.ownerGlobal, "got the right windowContext");
+    let [tab, closingPromise] = await tabOpened;
+    await closingPromise;
+    is(tab.linkedBrowser, null, "tab was opened and closed");
+  });
+});
+
+add_task(async function new_window() {
+  // Tests that a link that forces us to open a new window (by specifying a
+  // width and a height in window.open) opens a new window for the load,
+  // realizes that we need to close that window and returns the *original*
+  // window as the window context.
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let windowOpened = BrowserTestUtils.waitForNewWindow();
+
+    await BrowserTestUtils.synthesizeMouseAtCenter("#new_window", {}, browser);
+    let win = await windowOpened;
+    // Now allow request to complete:
+    fetch(SJS_URL + "?finish");
+
+    let windowContext = await dialogAppeared;
+    is(windowContext, browser.ownerGlobal, "got the right windowContext");
+
+    // The window should close on its own. If not, this test will time out.
+    await BrowserTestUtils.domWindowClosed(win);
+    ok(win.closed, "window was opened and closed");
+
+    is(
+      await fetch(SJS_URL + "?reset").then(r => r.text()),
+      "OK",
+      "Test reseted"
+    );
+  });
+});
+
+add_task(async function new_window_no_opener() {
+  // Tests that a link that forces us to open a new window (by specifying a
+  // width and a height in window.open) opens a new window for the load,
+  // realizes that we need to close that window and returns the *original*
+  // window as the window context.
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    browser
+  ) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let windowOpened = BrowserTestUtils.waitForNewWindow();
+
+    await BrowserTestUtils.synthesizeMouseAtCenter(
+      "#new_window_no_opener",
+      {},
+      browser
+    );
+    let win = await windowOpened;
+    // Now allow request to complete:
+    fetch(SJS_URL + "?finish");
+
+    await dialogAppeared;
+
+    // The window should close on its own. If not, this test will time out.
+    await BrowserTestUtils.domWindowClosed(win);
+    ok(win.closed, "window was opened and closed");
+
+    is(
+      await fetch(SJS_URL + "?reset").then(r => r.text()),
+      "OK",
+      "Test reseted"
+    );
+  });
+});
+
+add_task(async function nested_window_opens() {
+  // Tests that the window auto-closing feature works if the download is
+  // initiated by a window that, itself, has an opener (see bug 1373109).
+  await BrowserTestUtils.withNewTab({ gBrowser, url: PAGE_URL }, async function(
+    outerBrowser
+  ) {
+    let secondTabPromise = BrowserTestUtils.waitForNewTab(
+      gBrowser,
+      `${PAGE_URL}?newwin`,
+      true
+    );
+    BrowserTestUtils.synthesizeMouseAtCenter(
+      "#open_in_new_tab",
+      {},
+      outerBrowser
+    );
+    let secondTab = await secondTabPromise;
+    let nestedBrowser = secondTab.linkedBrowser;
+
+    await SpecialPowers.spawn(nestedBrowser, [], function() {
+      ok(content.opener, "this window has an opener");
+    });
+
+    await testNewTab(nestedBrowser);
+
+    isnot(
+      secondTab.linkedBrowser,
+      null,
+      "the page that triggered the download is still open"
+    );
+    BrowserTestUtils.removeTab(secondTab);
+  });
+});
+
+add_task(async function cleanup() {
+  // Unregister our factory from XPCOM and restore the original CID.
+  registrar.unregisterFactory(MOCK_HELPERAPP_DIALOG_CID, mockHelperAppService);
+  registrar.registerFactory(
+    HELPERAPP_DIALOG_CID,
+    "",
+    HELPERAPP_DIALOG_CONTRACT_ID,
+    null
+  );
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_download_always_ask_preferred_app.js b/uriloader/exthandler/tests/mochitest/browser_download_always_ask_preferred_app.js
new file mode 100644
index 0000000000..bd421d51f3
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_download_always_ask_preferred_app.js
@@ -0,0 +1,25 @@
+add_task(async function() {
+  // Create mocked objects for test
+  let launcher = createMockedObjects(false);
+  // Open helper app dialog with mocked launcher
+  let dlg = await openHelperAppDialog(launcher);
+  let doc = dlg.document;
+  let location = doc.getElementById("source");
+  let expectedValue = launcher.source.prePath;
+  if (location.value != expectedValue) {
+    info("Waiting for dialog to be populated.");
+    await BrowserTestUtils.waitForAttribute("value", location, expectedValue);
+  }
+  is(
+    doc.getElementById("mode").selectedItem.id,
+    "open",
+    "Should be opening the file."
+  );
+  ok(
+    !dlg.document.getElementById("openHandler").selectedItem.hidden,
+    "Should not have selected a hidden item."
+  );
+  let helperAppDialogHiddenPromise = BrowserTestUtils.windowClosed(dlg);
+  doc.getElementById("unknownContentType").cancelDialog();
+  await helperAppDialogHiddenPromise;
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_download_open_with_internal_handler.js b/uriloader/exthandler/tests/mochitest/browser_download_open_with_internal_handler.js
new file mode 100644
index 0000000000..ef7174f30f
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_download_open_with_internal_handler.js
@@ -0,0 +1,612 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+ChromeUtils.import("resource://gre/modules/Downloads.jsm", this);
+const { DownloadIntegration } = ChromeUtils.import(
+  "resource://gre/modules/DownloadIntegration.jsm"
+);
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+function waitForAcceptButtonToGetEnabled(doc) {
+  let dialog = doc.querySelector("#unknownContentType");
+  let button = dialog.getButton("accept");
+  return TestUtils.waitForCondition(
+    () => !button.disabled,
+    "Wait for Accept button to get enabled"
+  );
+}
+
+async function waitForPdfJS(browser, url) {
+  await SpecialPowers.pushPrefEnv({
+    set: [["pdfjs.eventBusDispatchToDOM", true]],
+  });
+  // Runs tests after all "load" event handlers have fired off
+  let loadPromise = BrowserTestUtils.waitForContentEvent(
+    browser,
+    "documentloaded",
+    false,
+    null,
+    true
+  );
+  await SpecialPowers.spawn(browser, [url], contentUrl => {
+    content.location = contentUrl;
+  });
+  return loadPromise;
+}
+
+add_task(async function setup() {
+  // Remove the security delay for the dialog during the test.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["security.dialog_enable_delay", 0],
+      ["browser.helperApps.showOpenOptionForPdfJS", true],
+      ["browser.helperApps.showOpenOptionForViewableInternally", true],
+    ],
+  });
+
+  // Restore handlers after the whole test has run
+  const mimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  const registerRestoreHandler = function(type, ext) {
+    const mimeInfo = mimeSvc.getFromTypeAndExtension(type, ext);
+    const existed = handlerSvc.exists(mimeInfo);
+    registerCleanupFunction(() => {
+      if (existed) {
+        handlerSvc.store(mimeInfo);
+      } else {
+        handlerSvc.remove(mimeInfo);
+      }
+    });
+  };
+  registerRestoreHandler("application/pdf", "pdf");
+  registerRestoreHandler("binary/octet-stream", "pdf");
+  registerRestoreHandler("application/unknown", "pdf");
+});
+
+/**
+ * Check that loading a PDF file with content-disposition: attachment
+ * shows an option to open with the internal handler, and that the
+ * internal option handler is not present when the download button
+ * is clicked from pdf.js.
+ */
+add_task(async function test_check_open_with_internal_handler() {
+  for (let file of [
+    "file_pdf_application_pdf.pdf",
+    "file_pdf_binary_octet_stream.pdf",
+  ]) {
+    info("Testing with " + file);
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    registerCleanupFunction(async () => {
+      await publicList.removeFinished();
+    });
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    // Add an extra tab after the loading tab so we can test that
+    // pdf.js is opened in the adjacent tab and not at the end of
+    // the tab strip.
+    let extraTab = await BrowserTestUtils.addTab(gBrowser, "about:blank");
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+    let doc = dialogWindow.document;
+    let internalHandlerRadio = doc.querySelector("#handleInternally");
+
+    await waitForAcceptButtonToGetEnabled(doc);
+
+    ok(!internalHandlerRadio.hidden, "The option should be visible for PDF");
+    ok(internalHandlerRadio.selected, "The option should be selected");
+
+    let downloadFinishedPromise = promiseDownloadFinished(publicList);
+    let newTabPromise = BrowserTestUtils.waitForNewTab(gBrowser);
+    let dialog = doc.querySelector("#unknownContentType");
+    let button = dialog.getButton("accept");
+    button.disabled = false;
+    dialog.acceptDialog();
+    info("waiting for new tab to open");
+    let newTab = await newTabPromise;
+
+    is(
+      newTab._tPos - 1,
+      loadingTab._tPos,
+      "pdf.js should be opened in an adjacent tab"
+    );
+
+    await ContentTask.spawn(newTab.linkedBrowser, null, async () => {
+      await ContentTaskUtils.waitForCondition(
+        () => content.document.readyState == "complete"
+      );
+    });
+
+    let publicDownloads = await publicList.getAll();
+    is(
+      publicDownloads.length,
+      1,
+      "download should appear in publicDownloads list"
+    );
+
+    let download = await downloadFinishedPromise;
+
+    let subdialogPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    // Current tab has file: URI and TEST_PATH is http uri, so uri will be different
+    BrowserTestUtils.loadURI(newTab.linkedBrowser, TEST_PATH + file);
+    let subDialogWindow = await subdialogPromise;
+    let subDoc = subDialogWindow.document;
+    // Prevent racing with initialization of the dialog and make sure that
+    // the final state of the dialog has the correct visibility of the internal-handler option.
+    await waitForAcceptButtonToGetEnabled(subDoc);
+    let subInternalHandlerRadio = subDoc.querySelector("#handleInternally");
+    ok(
+      !subInternalHandlerRadio.hidden,
+      "This option should be shown when the dialog is shown for another PDF"
+    );
+    // Cancel dialog
+    subDoc.querySelector("#unknownContentType").cancelDialog();
+
+    subdialogPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    await SpecialPowers.spawn(newTab.linkedBrowser, [], async () => {
+      let downloadButton;
+      await ContentTaskUtils.waitForCondition(() => {
+        downloadButton = content.document.querySelector("#download");
+        return !!downloadButton;
+      });
+      ok(downloadButton, "Download button should be present in pdf.js");
+      downloadButton.click();
+    });
+    info(
+      "Waiting for unknown content type dialog to appear from pdf.js download button click"
+    );
+    subDialogWindow = await subdialogPromise;
+    subDoc = subDialogWindow.document;
+    // Prevent racing with initialization of the dialog and make sure that
+    // the final state of the dialog has the correct visibility of the internal-handler option.
+    await waitForAcceptButtonToGetEnabled(subDoc);
+    subInternalHandlerRadio = subDoc.querySelector("#handleInternally");
+    ok(
+      subInternalHandlerRadio.hidden,
+      "The option should be hidden when the dialog is opened from pdf.js"
+    );
+    subDoc.querySelector("#open").click();
+
+    let tabOpenListener = () => {
+      ok(
+        false,
+        "A new tab should not be opened when accepting the dialog with 'open-with-external-app' chosen"
+      );
+    };
+    gBrowser.tabContainer.addEventListener("TabOpen", tabOpenListener);
+
+    let oldLaunchFile = DownloadIntegration.launchFile;
+    let waitForLaunchFileCalled = new Promise(resolve => {
+      DownloadIntegration.launchFile = async () => {
+        ok(true, "The file should be launched with an external application");
+        resolve();
+      };
+    });
+
+    downloadFinishedPromise = promiseDownloadFinished(publicList);
+
+    info("Accepting the dialog");
+    subDoc.querySelector("#unknownContentType").acceptDialog();
+    info("Waiting until DownloadIntegration.launchFile is called");
+    await waitForLaunchFileCalled;
+    DownloadIntegration.launchFile = oldLaunchFile;
+
+    // Remove the first file (can't do this sooner or the second load fails):
+    if (download?.target.exists) {
+      try {
+        info("removing " + download.target.path);
+        await IOUtils.remove(download.target.path);
+      } catch (ex) {
+        /* ignore */
+      }
+    }
+
+    gBrowser.tabContainer.removeEventListener("TabOpen", tabOpenListener);
+    BrowserTestUtils.removeTab(loadingTab);
+    BrowserTestUtils.removeTab(newTab);
+    BrowserTestUtils.removeTab(extraTab);
+
+    // Remove the remaining file once complete.
+    download = await downloadFinishedPromise;
+    if (download?.target.exists) {
+      try {
+        info("removing " + download.target.path);
+        await IOUtils.remove(download.target.path);
+      } catch (ex) {
+        /* ignore */
+      }
+    }
+    await publicList.removeFinished();
+  }
+});
+
+/**
+ * Test that choosing to open in an external application doesn't
+ * open the PDF into pdf.js
+ */
+add_task(async function test_check_open_with_external_application() {
+  for (let file of [
+    "file_pdf_application_pdf.pdf",
+    "file_pdf_binary_octet_stream.pdf",
+  ]) {
+    info("Testing with " + file);
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    registerCleanupFunction(async () => {
+      await publicList.removeFinished();
+    });
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+
+    let oldLaunchFile = DownloadIntegration.launchFile;
+    let waitForLaunchFileCalled = new Promise(resolve => {
+      DownloadIntegration.launchFile = () => {
+        ok(true, "The file should be launched with an external application");
+        resolve();
+      };
+    });
+
+    let doc = dialogWindow.document;
+    await waitForAcceptButtonToGetEnabled(doc);
+    let dialog = doc.querySelector("#unknownContentType");
+    doc.querySelector("#open").click();
+    let button = dialog.getButton("accept");
+    button.disabled = false;
+    info("Accepting the dialog");
+    dialog.acceptDialog();
+    info("Waiting until DownloadIntegration.launchFile is called");
+    await waitForLaunchFileCalled;
+    DownloadIntegration.launchFile = oldLaunchFile;
+
+    let publicDownloads = await publicList.getAll();
+    is(
+      publicDownloads.length,
+      1,
+      "download should appear in publicDownloads list"
+    );
+    let download = publicDownloads[0];
+    ok(
+      !download.launchWhenSucceeded,
+      "launchWhenSucceeded should be false after launchFile is called"
+    );
+
+    BrowserTestUtils.removeTab(loadingTab);
+    if (download?.target.exists) {
+      try {
+        info("removing " + download.target.path);
+        await IOUtils.remove(download.target.path);
+      } catch (ex) {
+        /* ignore */
+      }
+    }
+    await publicList.removeFinished();
+  }
+});
+
+/**
+ * Test that choosing to open a PDF with an external application works and
+ * then downloading the same file again and choosing Open with Firefox opens
+ * the download in Firefox.
+ */
+add_task(async function test_check_open_with_external_then_internal() {
+  // This test only runs on Windows because appPicker.xhtml is only used on Windows.
+  if (AppConstants.platform != "win") {
+    return;
+  }
+
+  // This test covers a bug that only occurs when the mimeInfo is set to Always Ask
+  const mimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  const mimeInfo = mimeSvc.getFromTypeAndExtension("application/pdf", "pdf");
+  mimeInfo.preferredAction = mimeInfo.alwaysAsk;
+  mimeInfo.alwaysAskBeforeHandling = true;
+  handlerSvc.store(mimeInfo);
+
+  for (let [file, mimeType] of [
+    ["file_pdf_application_pdf.pdf", "application/pdf"],
+    ["file_pdf_binary_octet_stream.pdf", "binary/octet-stream"],
+    ["file_pdf_application_unknown.pdf", "application/unknown"],
+  ]) {
+    info("Testing with " + file);
+    let originalMimeInfo = mimeSvc.getFromTypeAndExtension(mimeType, "pdf");
+
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    registerCleanupFunction(async () => {
+      await publicList.removeFinished();
+    });
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    // Open a new tab to the PDF file which will trigger the Unknown Content Type dialog
+    // and choose to open the PDF with an external application.
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+
+    let oldLaunchFile = DownloadIntegration.launchFile;
+    let waitForLaunchFileCalled = new Promise(resolve => {
+      DownloadIntegration.launchFile = () => {
+        ok(true, "The file should be launched with an external application");
+        resolve();
+      };
+    });
+
+    let doc = dialogWindow.document;
+    await waitForAcceptButtonToGetEnabled(doc);
+    let dialog = doc.querySelector("#unknownContentType");
+    let openHandlerMenulist = doc.querySelector("#openHandler");
+    let originalDefaultHandler = openHandlerMenulist.label;
+    doc.querySelector("#open").click();
+    doc.querySelector("#openHandlerPopup").click();
+    let oldOpenDialog = dialogWindow.openDialog;
+    dialogWindow.openDialog = (location, unused2, unused3, params) => {
+      is(location, "chrome://global/content/appPicker.xhtml", "app picker");
+      let handlerApp = params.mimeInfo.possibleLocalHandlers.queryElementAt(
+        0,
+        Ci.nsILocalHandlerApp
+      );
+      ok(handlerApp.executable, "handlerApp should be executable");
+      ok(handlerApp.executable.isFile(), "handlerApp should be a file");
+      params.handlerApp = handlerApp;
+    };
+    doc.querySelector("#choose").click();
+    dialogWindow.openDialog = oldOpenDialog;
+    await TestUtils.waitForCondition(
+      () => originalDefaultHandler != openHandlerMenulist.label,
+      "waiting for openHandler to get updated"
+    );
+    let newDefaultHandler = openHandlerMenulist.label;
+    info(`was ${originalDefaultHandler}, now ${newDefaultHandler}`);
+    let button = dialog.getButton("accept");
+    button.disabled = false;
+    info("Accepting the dialog");
+    dialog.acceptDialog();
+    info("Waiting until DownloadIntegration.launchFile is called");
+    await waitForLaunchFileCalled;
+    BrowserTestUtils.removeTab(loadingTab);
+
+    // Now, open a new tab to the PDF file which will trigger the Unknown Content Type dialog
+    // and choose to open the PDF internally. The previously used external application should be shown as
+    // the external option.
+    dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+
+    DownloadIntegration.launchFile = () => {
+      ok(false, "The file should not be launched with an external application");
+    };
+
+    doc = dialogWindow.document;
+    await waitForAcceptButtonToGetEnabled(doc);
+    openHandlerMenulist = doc.querySelector("#openHandler");
+    is(openHandlerMenulist.label, newDefaultHandler, "'new' handler");
+    dialog = doc.querySelector("#unknownContentType");
+    doc.querySelector("#handleInternally").click();
+    info("Accepting the dialog");
+    button = dialog.getButton("accept");
+    button.disabled = false;
+    let newTabPromise = BrowserTestUtils.waitForNewTab(gBrowser);
+    dialog.acceptDialog();
+
+    info("waiting for new tab to open");
+    let newTab = await newTabPromise;
+
+    await ContentTask.spawn(newTab.linkedBrowser, null, async () => {
+      await ContentTaskUtils.waitForCondition(
+        () => content.document.readyState == "complete"
+      );
+    });
+
+    is(
+      newTab.linkedBrowser.contentPrincipal.origin,
+      "resource://pdf.js",
+      "PDF should be opened with pdf.js"
+    );
+
+    BrowserTestUtils.removeTab(loadingTab);
+    BrowserTestUtils.removeTab(newTab);
+
+    // Now trigger the dialog again and select the system
+    // default option to reset the state for the next iteration of the test.
+    // Reset the state for the next iteration of the test.
+    handlerSvc.store(originalMimeInfo);
+    DownloadIntegration.launchFile = oldLaunchFile;
+    let [download] = await publicList.getAll();
+    if (download?.target.exists) {
+      try {
+        info("removing " + download.target.path);
+        await IOUtils.remove(download.target.path);
+      } catch (ex) {
+        /* ignore */
+      }
+    }
+    await publicList.removeFinished();
+  }
+});
+
+/**
+ * Check that the "Open with internal handler" option is presented
+ * for other viewable internally types.
+ */
+add_task(
+  async function test_internal_handler_hidden_with_viewable_internally_type() {
+    for (let [file, checkDefault] of [
+      // The default for binary/octet-stream is changed by the PDF tests above,
+      // this may change given bug 1659008, so I'm just ignoring the default for now.
+      ["file_xml_attachment_binary_octet_stream.xml", false],
+      ["file_xml_attachment_test.xml", true],
+    ]) {
+      let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+      let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+        gBrowser,
+        TEST_PATH + file
+      );
+      let dialogWindow = await dialogWindowPromise;
+      is(
+        dialogWindow.location.href,
+        "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+        "Should have seen the unknown content dialogWindow."
+      );
+      let doc = dialogWindow.document;
+      let internalHandlerRadio = doc.querySelector("#handleInternally");
+
+      // Prevent racing with initialization of the dialog and make sure that
+      // the final state of the dialog has the correct visibility of the internal-handler option.
+      await waitForAcceptButtonToGetEnabled(doc);
+
+      ok(!internalHandlerRadio.hidden, "The option should be visible for XML");
+      if (checkDefault) {
+        ok(internalHandlerRadio.selected, "The option should be selected");
+      }
+
+      let dialog = doc.querySelector("#unknownContentType");
+      dialog.cancelDialog();
+      BrowserTestUtils.removeTab(loadingTab);
+    }
+  }
+);
+
+/**
+ * Check that the "Open with internal handler" option is not presented
+ * for non-PDF, non-viewable-internally types.
+ */
+add_task(async function test_internal_handler_hidden_with_other_type() {
+  let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+  let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TEST_PATH + "file_txt_attachment_test.txt"
+  );
+  let dialogWindow = await dialogWindowPromise;
+  is(
+    dialogWindow.location.href,
+    "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+    "Should have seen the unknown content dialogWindow."
+  );
+  let doc = dialogWindow.document;
+
+  // Prevent racing with initialization of the dialog and make sure that
+  // the final state of the dialog has the correct visibility of the internal-handler option.
+  await waitForAcceptButtonToGetEnabled(doc);
+
+  let internalHandlerRadio = doc.querySelector("#handleInternally");
+  ok(
+    internalHandlerRadio.hidden,
+    "The option should be hidden for unknown file type"
+  );
+
+  let dialog = doc.querySelector("#unknownContentType");
+  dialog.cancelDialog();
+  BrowserTestUtils.removeTab(loadingTab);
+});
+
+/**
+ * Check that the "Open with internal handler" option is not presented
+ * when the feature is disabled for PDFs.
+ */
+add_task(async function test_internal_handler_hidden_with_pdf_pref_disabled() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.helperApps.showOpenOptionForPdfJS", false]],
+  });
+  for (let file of [
+    "file_pdf_application_pdf.pdf",
+    "file_pdf_binary_octet_stream.pdf",
+  ]) {
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+    let doc = dialogWindow.document;
+
+    await waitForAcceptButtonToGetEnabled(doc);
+
+    let internalHandlerRadio = doc.querySelector("#handleInternally");
+    ok(
+      internalHandlerRadio.hidden,
+      "The option should be hidden for PDF when the pref is false"
+    );
+
+    let dialog = doc.querySelector("#unknownContentType");
+    dialog.cancelDialog();
+    BrowserTestUtils.removeTab(loadingTab);
+  }
+});
+
+/**
+ * Check that the "Open with internal handler" option is not presented
+ * for other viewable internally types when disabled.
+ */
+add_task(
+  async function test_internal_handler_hidden_with_viewable_internally_pref_disabled() {
+    await SpecialPowers.pushPrefEnv({
+      set: [["browser.helperApps.showOpenOptionForViewableInternally", false]],
+    });
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + "file_xml_attachment_test.xml"
+    );
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+    let doc = dialogWindow.document;
+
+    await waitForAcceptButtonToGetEnabled(doc);
+
+    let internalHandlerRadio = doc.querySelector("#handleInternally");
+    ok(
+      internalHandlerRadio.hidden,
+      "The option should be hidden for XML when the pref is false"
+    );
+
+    let dialog = doc.querySelector("#unknownContentType");
+    dialog.cancelDialog();
+    BrowserTestUtils.removeTab(loadingTab);
+  }
+);
diff --git a/uriloader/exthandler/tests/mochitest/browser_download_privatebrowsing.js b/uriloader/exthandler/tests/mochitest/browser_download_privatebrowsing.js
new file mode 100644
index 0000000000..02cf6c3941
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_download_privatebrowsing.js
@@ -0,0 +1,70 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Tests that downloads started from a private window by clicking on a link end
+ * up in the global list of private downloads (see bug 1367581).
+ */
+
+"use strict";
+
+ChromeUtils.import("resource://gre/modules/Downloads.jsm", this);
+ChromeUtils.import("resource://gre/modules/DownloadPaths.jsm", this);
+ChromeUtils.import("resource://testing-common/FileTestUtils.jsm", this);
+ChromeUtils.import("resource://testing-common/MockRegistrar.jsm", this);
+
+add_task(async function test_setup() {
+  // Save downloads to disk without showing the dialog.
+  let cid = MockRegistrar.register("@mozilla.org/helperapplauncherdialog;1", {
+    QueryInterface: ChromeUtils.generateQI(["nsIHelperAppLauncherDialog"]),
+    show(launcher) {
+      launcher.promptForSaveDestination();
+    },
+    promptForSaveToFileAsync(launcher) {
+      // The dialog should create the empty placeholder file.
+      let file = FileTestUtils.getTempFile();
+      file.create(Ci.nsIFile.NORMAL_FILE_TYPE, FileUtils.PERMS_FILE);
+      launcher.saveDestinationAvailable(file);
+    },
+  });
+  registerCleanupFunction(() => {
+    MockRegistrar.unregister(cid);
+  });
+});
+
+add_task(async function test_download_privatebrowsing() {
+  let privateList = await Downloads.getList(Downloads.PRIVATE);
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+
+  let win = await BrowserTestUtils.openNewBrowserWindow({ private: true });
+  try {
+    let tab = await BrowserTestUtils.openNewForegroundTab(
+      win.gBrowser,
+      `data:text/html,<a download href="data:text/plain,">download</a>`
+    );
+
+    let promiseNextPrivateDownload = new Promise(resolve => {
+      privateList.addView({
+        onDownloadAdded(download) {
+          privateList.removeView(this);
+          resolve(download);
+        },
+      });
+    });
+
+    await SpecialPowers.spawn(tab.linkedBrowser, [], async function() {
+      content.document.querySelector("a").click();
+    });
+
+    // Wait for the download to finish so the file can be safely deleted later.
+    let download = await promiseNextPrivateDownload;
+    await download.whenSucceeded();
+
+    // Clean up after checking that there are no new public downloads either.
+    let publicDownloads = await publicList.getAll();
+    Assert.equal(publicDownloads.length, 0);
+    await privateList.removeFinished();
+  } finally {
+    await BrowserTestUtils.closeWindow(win);
+  }
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_download_urlescape.js b/uriloader/exthandler/tests/mochitest/browser_download_urlescape.js
new file mode 100644
index 0000000000..ffab8146b6
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_download_urlescape.js
@@ -0,0 +1,75 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+var MockFilePicker = SpecialPowers.MockFilePicker;
+MockFilePicker.init(window);
+registerCleanupFunction(() => MockFilePicker.cleanup());
+
+/**
+ * Check downloading files URL-escapes content-disposition
+ * information when necessary.
+ */
+add_task(async function test_check_filename_urlescape() {
+  let pendingPromise;
+  let pendingTest = "";
+  let expectedFileName = "";
+  MockFilePicker.showCallback = function(fp) {
+    info(`${pendingTest} - Filepicker shown, checking filename`);
+    is(
+      fp.defaultString,
+      expectedFileName,
+      `${pendingTest} - Should have escaped filename`
+    );
+    ok(
+      pendingPromise,
+      `${pendingTest} - Should have expected this picker open.`
+    );
+    if (pendingPromise) {
+      pendingPromise.resolve();
+    }
+    return Ci.nsIFilePicker.returnCancel;
+  };
+  function runTestFor(fileName, selector) {
+    return BrowserTestUtils.withNewTab(TEST_PATH + fileName, async browser => {
+      expectedFileName = fileName;
+      let tabLabel = gBrowser.getTabForBrowser(browser).getAttribute("label");
+      ok(
+        tabLabel.startsWith(fileName),
+        `"${tabLabel}" should have been escaped.`
+      );
+
+      pendingTest = "save browser";
+      pendingPromise = PromiseUtils.defer();
+      // First try to save the browser
+      saveBrowser(browser);
+      await pendingPromise.promise;
+
+      // Next, try the context menu:
+      pendingTest = "save from context menu";
+      pendingPromise = PromiseUtils.defer();
+      let menu = document.getElementById("contentAreaContextMenu");
+      let menuShown = BrowserTestUtils.waitForEvent(menu, "popupshown");
+      BrowserTestUtils.synthesizeMouse(
+        selector,
+        5,
+        5,
+        { type: "contextmenu", button: 2 },
+        browser
+      );
+      await menuShown;
+      gContextMenu.saveMedia();
+      menu.hidePopup();
+      await pendingPromise.promise;
+      pendingPromise = null;
+    });
+  }
+  await runTestFor("file_with@@funny_name.png", "img");
+  await runTestFor("file_with[funny_name.webm", "video");
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_extension_correction.js b/uriloader/exthandler/tests/mochitest/browser_extension_correction.js
new file mode 100644
index 0000000000..b806ee9ace
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_extension_correction.js
@@ -0,0 +1,145 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+let gPathsToRemove = [];
+
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.download.useDownloadDir", true]],
+  });
+  registerCleanupFunction(async () => {
+    for (let path of gPathsToRemove) {
+      // IOUtils.remove ignores non-existing files out of the box.
+      await IOUtils.remove(path);
+    }
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    await publicList.removeFinished();
+  });
+});
+
+async function testLinkWithoutExtension(type, shouldHaveExtension) {
+  info("Checking " + type);
+
+  let task = function() {
+    return SpecialPowers.spawn(gBrowser.selectedBrowser, [type], mimetype => {
+      let link = content.document.createElement("a");
+      link.textContent = "Click me";
+      link.href = "data:" + mimetype + ",hello";
+      link.download = "somefile";
+      content.document.body.appendChild(link);
+      link.click();
+    });
+  };
+  await checkDownloadWithExtensionState(task, { type, shouldHaveExtension });
+}
+
+async function checkDownloadWithExtensionState(
+  task,
+  { type, shouldHaveExtension, expectedName = null }
+) {
+  let winPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+
+  await task();
+
+  info("Waiting for dialog.");
+  let win = await winPromise;
+
+  let actualName = win.document.getElementById("location").value;
+  if (shouldHaveExtension) {
+    expectedName ??= "somefile." + getMIMEInfoForType(type).primaryExtension;
+    is(actualName, expectedName, `${type} should get an extension`);
+  } else {
+    expectedName ??= "somefile";
+    is(actualName, expectedName, `${type} should not get an extension`);
+  }
+
+  let closedPromise = BrowserTestUtils.windowClosed(win);
+
+  if (shouldHaveExtension) {
+    // Wait for the download.
+    let publicList = await Downloads.getList(Downloads.PUBLIC);
+    let downloadFinishedPromise = promiseDownloadFinished(publicList);
+
+    // Then pick "save" in the dialog.
+    let dialog = win.document.getElementById("unknownContentType");
+    win.document.getElementById("save").click();
+    let button = dialog.getButton("accept");
+    button.disabled = false;
+    dialog.acceptDialog();
+
+    // Wait for the download to finish and check the extension is correct.
+    let download = await downloadFinishedPromise;
+    is(
+      PathUtils.filename(download.target.path),
+      expectedName,
+      `Downloaded file should also match ${expectedName}`
+    );
+    gPathsToRemove.push(download.target.path);
+    let pathToRemove = download.target.path;
+    // Avoid one file interfering with subsequent files.
+    await publicList.removeFinished();
+    await IOUtils.remove(pathToRemove);
+  } else {
+    // We just cancel out for files that would end up without a path, as we'd
+    // prompt for a filename.
+    win.close();
+  }
+  return closedPromise;
+}
+
+/**
+ * Check that for document types, images, videos and audio files,
+ * we enforce a useful extension.
+ */
+add_task(async function test_enforce_useful_extension() {
+  await BrowserTestUtils.withNewTab("data:text/html,", async browser => {
+    await testLinkWithoutExtension("image/png", true);
+    await testLinkWithoutExtension("audio/ogg", true);
+    await testLinkWithoutExtension("video/webm", true);
+    await testLinkWithoutExtension("application/msword", true);
+    await testLinkWithoutExtension("application/pdf", true);
+
+    await testLinkWithoutExtension("application/x-gobbledygook", false);
+    await testLinkWithoutExtension("application/octet-stream", false);
+    await testLinkWithoutExtension("binary/octet-stream", false);
+    await testLinkWithoutExtension("application/x-msdownload", false);
+  });
+});
+
+/**
+ * Check that we still use URL extension info when we don't have anything else,
+ * despite bogus local info.
+ */
+add_task(async function test_broken_saved_handlerinfo_and_useless_mimetypes() {
+  let bogusType = getMIMEInfoForType("binary/octet-stream");
+  bogusType.setFileExtensions(["jpg"]);
+  let handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  handlerSvc.store(bogusType);
+  let tabToClean = null;
+  let task = function() {
+    return BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + "file_as.exe?foo=bar"
+    ).then(tab => {
+      return (tabToClean = tab);
+    });
+  };
+  await checkDownloadWithExtensionState(task, {
+    type: "binary/octet-stream",
+    shouldHaveExtension: true,
+    expectedName: "file_as.exe",
+  });
+  // Downloads should really close their tabs...
+  if (tabToClean?.isConnected) {
+    BrowserTestUtils.removeTab(tabToClean);
+  }
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_first_prompt_not_blocked_without_user_interaction.js b/uriloader/exthandler/tests/mochitest/browser_first_prompt_not_blocked_without_user_interaction.js
new file mode 100644
index 0000000000..b6f401e5e1
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_first_prompt_not_blocked_without_user_interaction.js
@@ -0,0 +1,70 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+add_task(setupMailHandler);
+
+add_task(async function test_open_without_user_interaction() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["dom.disable_open_during_load", true],
+      ["dom.block_external_protocol_in_iframes", true],
+      ["dom.delay.block_external_protocol_in_iframes.enabled", false],
+    ],
+  });
+
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
+
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+
+  BrowserTestUtils.loadURI(
+    tab.linkedBrowser,
+    TEST_PATH + "file_external_protocol_iframe.html"
+  );
+
+  let dialog = await dialogWindowPromise;
+  ok(dialog, "Should show the dialog even without user interaction");
+
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+
+  // Adding another iframe without user interaction should be blocked.
+  let blockedWarning = new Promise(resolve => {
+    Services.console.registerListener(function onMessage(msg) {
+      let { message, logLevel } = msg;
+      if (logLevel != Ci.nsIConsoleMessage.warn) {
+        return;
+      }
+      if (!message.includes("Iframe with external protocol was blocked")) {
+        return;
+      }
+      Services.console.unregisterListener(onMessage);
+      resolve();
+    });
+  });
+
+  info("Adding another frame without user interaction");
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async function() {
+    let frame = content.document.createElement("iframe");
+    frame.src = "mailto:foo@baz.com";
+    content.document.body.appendChild(frame);
+  });
+
+  await blockedWarning;
+
+  info("Removing tab to close the dialog.");
+  gBrowser.removeTab(tab);
+  await dialogClosedPromise;
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_open_internal_choice_persistence.js b/uriloader/exthandler/tests/mochitest/browser_open_internal_choice_persistence.js
new file mode 100644
index 0000000000..a36443edd1
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_open_internal_choice_persistence.js
@@ -0,0 +1,255 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+ChromeUtils.import("resource://gre/modules/Downloads.jsm", this);
+const { DownloadIntegration } = ChromeUtils.import(
+  "resource://gre/modules/DownloadIntegration.jsm"
+);
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+function waitForAcceptButtonToGetEnabled(doc) {
+  let dialog = doc.querySelector("#unknownContentType");
+  let button = dialog.getButton("accept");
+  return TestUtils.waitForCondition(
+    () => !button.disabled,
+    "Wait for Accept button to get enabled"
+  );
+}
+
+async function waitForPdfJS(browser, url) {
+  await SpecialPowers.pushPrefEnv({
+    set: [["pdfjs.eventBusDispatchToDOM", true]],
+  });
+  // Runs tests after all "load" event handlers have fired off
+  let loadPromise = BrowserTestUtils.waitForContentEvent(
+    browser,
+    "documentloaded",
+    false,
+    null,
+    true
+  );
+  await SpecialPowers.spawn(browser, [url], contentUrl => {
+    content.location = contentUrl;
+  });
+  return loadPromise;
+}
+
+add_task(async function setup() {
+  // Remove the security delay for the dialog during the test.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["security.dialog_enable_delay", 0],
+      ["browser.helperApps.showOpenOptionForPdfJS", true],
+      ["browser.helperApps.showOpenOptionForViewableInternally", true],
+    ],
+  });
+
+  // Restore handlers after the whole test has run
+  const registerRestoreHandler = function(type, ext) {
+    const mimeInfo = gMimeSvc.getFromTypeAndExtension(type, ext);
+    const existed = gHandlerSvc.exists(mimeInfo);
+    registerCleanupFunction(() => {
+      if (existed) {
+        gHandlerSvc.store(mimeInfo);
+      } else {
+        gHandlerSvc.remove(mimeInfo);
+      }
+    });
+  };
+  registerRestoreHandler("application/pdf", "pdf");
+});
+
+const { handleInternally, saveToDisk, useSystemDefault } = Ci.nsIHandlerInfo;
+
+const kTestCases = [
+  {
+    description:
+      "Saving to disk when internal handling is the default shouldn't change prefs.",
+    preDialogState: { preferredAction: handleInternally, alwaysAsk: false },
+    dialogActions(doc) {
+      let saveItem = doc.querySelector("#save");
+      saveItem.click();
+      ok(saveItem.selected, "The 'save' option should now be selected");
+    },
+    expectTab: false,
+    expectLaunch: false,
+    expectedPreferredAction: handleInternally,
+    expectedAsk: false,
+  },
+  {
+    description:
+      "Opening externally when internal handling is the default shouldn't change prefs.",
+    preDialogState: { preferredAction: handleInternally, alwaysAsk: false },
+    dialogActions(doc) {
+      let openItem = doc.querySelector("#open");
+      openItem.click();
+      ok(openItem.selected, "The 'save' option should now be selected");
+    },
+    expectTab: false,
+    expectLaunch: true,
+    expectedPreferredAction: handleInternally,
+    expectedAsk: false,
+  },
+  {
+    description:
+      "Saving to disk when internal handling is the default *should* change prefs if checkbox is ticked.",
+    preDialogState: { preferredAction: handleInternally, alwaysAsk: false },
+    dialogActions(doc) {
+      let saveItem = doc.querySelector("#save");
+      saveItem.click();
+      ok(saveItem.selected, "The 'save' option should now be selected");
+      let checkbox = doc.querySelector("#rememberChoice");
+      checkbox.checked = true;
+      checkbox.doCommand();
+    },
+    expectTab: false,
+    expectLaunch: false,
+    expectedPreferredAction: saveToDisk,
+    expectedAsk: false,
+  },
+  {
+    description:
+      "Saving to disk when asking is the default should change persisted default.",
+    preDialogState: { preferredAction: handleInternally, alwaysAsk: true },
+    dialogActions(doc) {
+      let saveItem = doc.querySelector("#save");
+      saveItem.click();
+      ok(saveItem.selected, "The 'save' option should now be selected");
+    },
+    expectTab: false,
+    expectLaunch: false,
+    expectedPreferredAction: saveToDisk,
+    expectedAsk: true,
+  },
+  {
+    description:
+      "Opening externally when asking is the default should change persisted default.",
+    preDialogState: { preferredAction: handleInternally, alwaysAsk: true },
+    dialogActions(doc) {
+      let openItem = doc.querySelector("#open");
+      openItem.click();
+      ok(openItem.selected, "The 'save' option should now be selected");
+    },
+    expectTab: false,
+    expectLaunch: true,
+    expectedPreferredAction: useSystemDefault,
+    expectedAsk: true,
+  },
+];
+
+function ensureMIMEState({ preferredAction, alwaysAsk }) {
+  const mimeInfo = gMimeSvc.getFromTypeAndExtension("application/pdf", "pdf");
+  mimeInfo.preferredAction = preferredAction;
+  mimeInfo.alwaysAskBeforeHandling = alwaysAsk;
+  gHandlerSvc.store(mimeInfo);
+}
+
+/**
+ * Test that if we have PDFs set to handle internally, and the user chooses to
+ * do something else with it, we do not alter the saved state.
+ */
+add_task(async function test_check_saving_handler_choices() {
+  let publicList = await Downloads.getList(Downloads.PUBLIC);
+  registerCleanupFunction(async () => {
+    await publicList.removeFinished();
+  });
+  for (let testCase of kTestCases) {
+    let file = "file_pdf_application_pdf.pdf";
+    info("Testing with " + file + "; " + testCase.description);
+    ensureMIMEState(testCase.preDialogState);
+
+    let dialogWindowPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+    let loadingTab = await BrowserTestUtils.openNewForegroundTab(
+      gBrowser,
+      TEST_PATH + file
+    );
+    let dialogWindow = await dialogWindowPromise;
+    is(
+      dialogWindow.location.href,
+      "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+      "Should have seen the unknown content dialogWindow."
+    );
+    let doc = dialogWindow.document;
+    let internalHandlerRadio = doc.querySelector("#handleInternally");
+
+    await waitForAcceptButtonToGetEnabled(doc);
+
+    ok(!internalHandlerRadio.hidden, "The option should be visible for PDF");
+    ok(
+      internalHandlerRadio.selected,
+      "The Firefox option should be selected by default"
+    );
+
+    const { expectTab, expectLaunch, description } = testCase;
+    // Prep to intercept things so we only see the results we want.
+    let tabOpenListener = ev => {
+      ok(
+        expectTab,
+        `A new tab should ${expectTab ? "" : "not "}be opened - ${description}`
+      );
+      BrowserTestUtils.removeTab(ev.target);
+    };
+    gBrowser.tabContainer.addEventListener("TabOpen", tabOpenListener);
+
+    let oldLaunchFile = DownloadIntegration.launchFile;
+    let fileLaunched = PromiseUtils.defer();
+    DownloadIntegration.launchFile = () => {
+      ok(
+        expectLaunch,
+        `The file should ${
+          expectLaunch ? "" : "not "
+        }be launched with an external application - ${description}`
+      );
+      fileLaunched.resolve();
+    };
+    let downloadFinishedPromise = promiseDownloadFinished(publicList);
+
+    await testCase.dialogActions(doc);
+
+    let dialog = doc.querySelector("#unknownContentType");
+    dialog.acceptDialog();
+
+    let download = await downloadFinishedPromise;
+    if (expectLaunch) {
+      await fileLaunched.promise;
+    }
+    DownloadIntegration.launchFile = oldLaunchFile;
+    gBrowser.tabContainer.removeEventListener("TabOpen", tabOpenListener);
+
+    is(
+      (await publicList.getAll()).length,
+      1,
+      "download should appear in public list"
+    );
+
+    // Check mime info:
+    const mimeInfo = gMimeSvc.getFromTypeAndExtension("application/pdf", "pdf");
+    gHandlerSvc.fillHandlerInfo(mimeInfo, "");
+    is(
+      mimeInfo.preferredAction,
+      testCase.expectedPreferredAction,
+      "preferredAction - " + description
+    );
+    is(
+      mimeInfo.alwaysAskBeforeHandling,
+      testCase.expectedAsk,
+      "alwaysAsk - " + description
+    );
+
+    BrowserTestUtils.removeTab(loadingTab);
+    await publicList.removeFinished();
+    if (download?.target.exists) {
+      try {
+        await IOUtils.remove(download.target.path);
+      } catch (ex) {
+        /* ignore */
+      }
+    }
+  }
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog.js b/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog.js
new file mode 100644
index 0000000000..5f60e39bb1
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog.js
@@ -0,0 +1,398 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const TEST_PATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content",
+  "https://example.com"
+);
+
+const CONTENT_HANDLING_URL =
+  "chrome://mozapps/content/handling/appChooser.xhtml";
+
+add_task(setupMailHandler);
+
+/**
+ * Check that if we open the protocol handler dialog from a subframe, we close
+ * it when closing the tab.
+ */
+add_task(async function test_closed_by_tab_closure() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TEST_PATH + "file_nested_protocol_request.html"
+  );
+
+  // Wait for the window and then click the link.
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+
+  BrowserTestUtils.synthesizeMouseAtCenter(
+    "a:link",
+    {},
+    tab.linkedBrowser.browsingContext.children[0]
+  );
+
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog URL is as expected"
+  );
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+
+  info("Removing tab to close the dialog.");
+  gBrowser.removeTab(tab);
+  await dialogClosedPromise;
+  ok(!dialog._frame.contentWindow, "The dialog should have been closed.");
+});
+
+/**
+ * Check that if we open the protocol handler dialog from a subframe, we close
+ * it when navigating the tab to a non-same-origin URL.
+ */
+add_task(async function test_closed_by_tab_navigation() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TEST_PATH + "file_nested_protocol_request.html"
+  );
+
+  // Wait for the window and then click the link.
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+
+  BrowserTestUtils.synthesizeMouseAtCenter(
+    "a:link",
+    {},
+    tab.linkedBrowser.browsingContext.children[0]
+  );
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog URL is as expected"
+  );
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  info(
+    "Set up unload handler to ensure we don't break when the window global gets cleared"
+  );
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async function() {
+    content.addEventListener("unload", function() {});
+  });
+
+  info("Navigating tab to a different but same origin page.");
+  BrowserTestUtils.loadURI(tab.linkedBrowser, TEST_PATH);
+  await BrowserTestUtils.browserLoaded(tab.linkedBrowser, false, TEST_PATH);
+  ok(dialog._frame.contentWindow, "Dialog should stay open.");
+
+  // The use of weak references in various parts of the code means that we're
+  // susceptible to dropping crucial bits of our implementation on the floor,
+  // if they get GC'd, and then the test hangs.
+  // Do a bunch of GC/CC runs so that if we ever break, it's deterministic.
+  let numCycles = 3;
+  for (let i = 0; i < numCycles; i++) {
+    Cu.forceGC();
+    Cu.forceCC();
+  }
+
+  info("Now navigate to a cross-origin page.");
+  const CROSS_ORIGIN_TEST_PATH = TEST_PATH.replace(".com", ".org");
+  BrowserTestUtils.loadURI(tab.linkedBrowser, CROSS_ORIGIN_TEST_PATH);
+  let loadPromise = BrowserTestUtils.browserLoaded(
+    tab.linkedBrowser,
+    false,
+    CROSS_ORIGIN_TEST_PATH
+  );
+  await dialogClosedPromise;
+  ok(!dialog._frame.contentWindow, "The dialog should have been closed.");
+
+  // Avoid errors from aborted loads by waiting for it to finish.
+  await loadPromise;
+  gBrowser.removeTab(tab);
+});
+
+/**
+ * Check that we cannot open more than one of these dialogs.
+ */
+add_task(async function test_multiple_dialogs() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    TEST_PATH + "file_nested_protocol_request.html"
+  );
+
+  // Wait for the window and then click the link.
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+  BrowserTestUtils.synthesizeMouseAtCenter(
+    "a:link",
+    {},
+    tab.linkedBrowser.browsingContext.children[0]
+  );
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog URL is as expected"
+  );
+
+  // Navigate the parent frame:
+  await ContentTask.spawn(tab.linkedBrowser, [], () =>
+    content.eval("location.href = 'mailto:help@example.com'")
+  );
+
+  // Wait for a few ticks:
+  // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+  await new Promise(r => setTimeout(r, 100));
+  // Check we only have one dialog
+
+  let tabDialogBox = gBrowser.getTabDialogBox(tab.linkedBrowser);
+  let dialogs = tabDialogBox
+    .getTabDialogManager()
+    ._dialogs.filter(d => d._openedURL == CONTENT_HANDLING_URL);
+
+  is(dialogs.length, 1, "Should only have 1 dialog open");
+
+  // Close the dialog:
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  dialog.close();
+  dialog = await dialogClosedPromise;
+
+  ok(!dialog._openedURL, "The dialog should have been closed.");
+
+  // Then reopen the dialog again, to make sure we don't keep blocking:
+  dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+  BrowserTestUtils.synthesizeMouseAtCenter(
+    "a:link",
+    {},
+    tab.linkedBrowser.browsingContext.children[0]
+  );
+  dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Second dialog URL is as expected"
+  );
+
+  dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  info("Removing tab to close the dialog.");
+  gBrowser.removeTab(tab);
+  await dialogClosedPromise;
+  ok(!dialog._frame.contentWindow, "The dialog should have been closed again.");
+});
+
+/**
+ * Check that navigating invisible frames to external-proto URLs
+ * is handled correctly.
+ */
+add_task(async function invisible_iframes() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "https://example.com/"
+  );
+
+  // Ensure we notice the dialog opening:
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+  await SpecialPowers.spawn(tab.linkedBrowser, [], function() {
+    let frame = content.document.createElement("iframe");
+    frame.style.display = "none";
+    frame.src = "mailto:help@example.com";
+    content.document.body.append(frame);
+  });
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog opens as expected for invisible iframe"
+  );
+  // Close the dialog:
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  dialog.close();
+  await dialogClosedPromise;
+  gBrowser.removeTab(tab);
+});
+
+/**
+ * Check that nested iframes are handled correctly.
+ */
+add_task(async function nested_iframes() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "https://example.com/"
+  );
+
+  // Ensure we notice the dialog opening:
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+  let innerLoaded = BrowserTestUtils.browserLoaded(
+    tab.linkedBrowser,
+    true,
+    "https://example.org/"
+  );
+  info("Constructing top frame");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], function() {
+    let frame = content.document.createElement("iframe");
+    frame.src = "https://example.org/"; // cross-origin frame.
+    content.document.body.prepend(frame);
+
+    content.eval(
+      `window.addEventListener("message", e => e.source.location = "mailto:help@example.com");`
+    );
+  });
+
+  await innerLoaded;
+  let parentBC = tab.linkedBrowser.browsingContext;
+
+  info("Creating innermost frame");
+  await SpecialPowers.spawn(parentBC.children[0], [], async function() {
+    let innerFrame = content.document.createElement("iframe");
+    let frameLoaded = ContentTaskUtils.waitForEvent(innerFrame, "load", true);
+    content.document.body.prepend(innerFrame);
+    await frameLoaded;
+  });
+
+  info("Posting event from innermost frame");
+  await SpecialPowers.spawn(
+    parentBC.children[0].children[0],
+    [],
+    async function() {
+      // Top browsing context needs reference to the innermost, which is cross origin.
+      content.eval("top.postMessage('hello', '*')");
+    }
+  );
+
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog opens as expected for deeply nested cross-origin iframe"
+  );
+  // Close the dialog:
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  dialog.close();
+  await dialogClosedPromise;
+  gBrowser.removeTab(tab);
+});
+
+add_task(async function test_oop_iframe() {
+  const URI = `data:text/html,<div id="root"><iframe src="http://example.com/document-builder.sjs?html=<a href='mailto:help@example.com'>Mail it</a>"></iframe></div>`;
+
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, URI);
+
+  // Wait for the window and then click the link.
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+
+  BrowserTestUtils.synthesizeMouseAtCenter(
+    "a:link",
+    {},
+    tab.linkedBrowser.browsingContext.children[0]
+  );
+
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog URL is as expected"
+  );
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+
+  info("Removing tab to close the dialog.");
+  gBrowser.removeTab(tab);
+  await dialogClosedPromise;
+  ok(!dialog._frame.contentWindow, "The dialog should have been closed.");
+});
+
+/**
+ * Check that a cross-origin iframe can navigate the top frame
+ * to an external protocol.
+ */
+add_task(async function xorigin_iframe_can_navigate_top() {
+  let tab = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    "https://example.com/"
+  );
+
+  // Ensure we notice the dialog opening:
+  let dialogWindowPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    true
+  );
+  let innerLoaded = BrowserTestUtils.browserLoaded(
+    tab.linkedBrowser,
+    true,
+    "https://example.org/"
+  );
+  info("Constructing frame");
+  await SpecialPowers.spawn(tab.linkedBrowser, [], function() {
+    let frame = content.document.createElement("iframe");
+    frame.src = "https://example.org/"; // cross-origin frame.
+    content.document.body.prepend(frame);
+  });
+  await innerLoaded;
+
+  info("Navigating top bc from frame");
+  let parentBC = tab.linkedBrowser.browsingContext;
+  await SpecialPowers.spawn(parentBC.children[0], [], async function() {
+    content.eval("window.top.location.href = 'mailto:example@example.com';");
+  });
+
+  let dialog = await dialogWindowPromise;
+
+  is(
+    dialog._frame.contentDocument.location.href,
+    CONTENT_HANDLING_URL,
+    "Dialog opens as expected for navigating the top frame from an x-origin frame."
+  );
+  // Close the dialog:
+  let dialogClosedPromise = waitForProtocolAppChooserDialog(
+    tab.linkedBrowser,
+    false
+  );
+  dialog.close();
+  await dialogClosedPromise;
+  gBrowser.removeTab(tab);
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog_permission.js b/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog_permission.js
new file mode 100644
index 0000000000..7050616dc3
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_protocol_ask_dialog_permission.js
@@ -0,0 +1,754 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+ChromeUtils.import(
+  "resource://testing-common/HandlerServiceTestUtils.jsm",
+  this
+);
+
+let gHandlerService = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+  Ci.nsIHandlerService
+);
+
+// Testing multiple protocol / origin combinations takes long on debug.
+requestLongerTimeout(3);
+
+const DIALOG_URL_APP_CHOOSER =
+  "chrome://mozapps/content/handling/appChooser.xhtml";
+const DIALOG_URL_PERMISSION =
+  "chrome://mozapps/content/handling/permissionDialog.xhtml";
+
+const PROTOCOL_HANDLER_OPEN_PERM_KEY = "open-protocol-handler";
+const PERMISSION_KEY_DELIMITER = "^";
+
+const TEST_PROTOS = ["foo", "bar"];
+
+let testDir = getChromeDir(getResolvedURI(gTestPath));
+
+const ORIGIN1 = "https://example.com";
+const ORIGIN2 = "https://example.org";
+const ORIGIN3 = Services.io.newFileURI(testDir).spec;
+const PRINCIPAL1 = Services.scriptSecurityManager.createContentPrincipalFromOrigin(
+  ORIGIN1
+);
+const PRINCIPAL2 = Services.scriptSecurityManager.createContentPrincipalFromOrigin(
+  ORIGIN2
+);
+const PRINCIPAL3 = Services.scriptSecurityManager.createContentPrincipalFromOrigin(
+  ORIGIN3
+);
+
+let testExtension;
+
+/**
+ * Get the open protocol handler permission key for a given protocol scheme.
+ * @param {string} aProtocolScheme - Scheme of protocol to construct permission
+ * key with.
+ */
+function getSkipProtoDialogPermissionKey(aProtocolScheme) {
+  return (
+    PROTOCOL_HANDLER_OPEN_PERM_KEY + PERMISSION_KEY_DELIMITER + aProtocolScheme
+  );
+}
+
+/**
+ * Creates dummy web protocol handlers used for testing.
+ */
+function initTestHandlers() {
+  TEST_PROTOS.forEach(scheme => {
+    let webHandler = Cc[
+      "@mozilla.org/uriloader/web-handler-app;1"
+    ].createInstance(Ci.nsIWebHandlerApp);
+    webHandler.name = scheme + "Handler";
+    webHandler.uriTemplate = ORIGIN1 + "/?url=%s";
+
+    let handlerInfo = HandlerServiceTestUtils.getBlankHandlerInfo(scheme);
+    handlerInfo.possibleApplicationHandlers.appendElement(webHandler);
+    handlerInfo.preferredApplicationHandler = webHandler;
+
+    gHandlerService.store(handlerInfo);
+  });
+}
+
+/**
+ * Update whether the protocol handler dialog is shown for our test protocol +
+ * handler.
+ * @param {string} scheme - Scheme of the protocol to change the ask state for.
+ * @param {boolean} ask - true => show dialog, false => skip dialog.
+ */
+function updateAlwaysAsk(scheme, ask) {
+  let handlerInfo = HandlerServiceTestUtils.getHandlerInfo(scheme);
+  handlerInfo.alwaysAskBeforeHandling = ask;
+  gHandlerService.store(handlerInfo);
+}
+
+/**
+ * Test whether the protocol handler dialog is set to show for our
+ * test protocol + handler.
+ * @param {string} scheme - Scheme of the protocol to test the ask state for.
+ * @param {boolean} ask - true => show dialog, false => skip dialog.
+ */
+function testAlwaysAsk(scheme, ask) {
+  is(
+    HandlerServiceTestUtils.getHandlerInfo(scheme).alwaysAskBeforeHandling,
+    ask,
+    "Should have correct alwaysAsk state."
+  );
+}
+
+/**
+ * Open a test URL with the desired scheme.
+ * By default the load is triggered by the content principal of the browser.
+ * @param {MozBrowser} browser - Browser to load the test URL in.
+ * @param {string} scheme - Scheme of the test URL.
+ * @param {Object} [opts] - Options for the triggering principal.
+ * @param {nsIPrincipal} [opts.triggeringPrincipal] - Principal to trigger the
+ * load with. Defaults to the browsers content principal.
+ * @param {boolean} [opts.useNullPrincipal] - If true, we will trigger the load
+ * with a null principal.
+ * @param {boolean} [opts.useExtensionPrincipal] - If true, we will trigger the
+ * load with an extension.
+ * @param {boolean} [opts.omitTriggeringPrincipal] - If true, we will directly
+ * call the protocol handler dialogs without a principal.
+ */
+async function triggerOpenProto(
+  browser,
+  scheme,
+  {
+    triggeringPrincipal = browser.contentPrincipal,
+    useNullPrincipal = false,
+    useExtensionPrincipal = false,
+    omitTriggeringPrincipal = false,
+  } = {}
+) {
+  let uri = `${scheme}://test`;
+
+  if (useNullPrincipal) {
+    // Create and load iframe with data URI.
+    // This will be a null principal.
+    ContentTask.spawn(browser, { uri }, args => {
+      let frame = content.document.createElement("iframe");
+      frame.src = `data:text/html,<script>location.href="${args.uri}"</script>`;
+      content.document.body.appendChild(frame);
+    });
+    return;
+  }
+
+  if (useExtensionPrincipal) {
+    const EXTENSION_DATA = {
+      manifest: {
+        content_scripts: [
+          {
+            matches: [browser.currentURI.spec],
+            js: ["navigate.js"],
+          },
+        ],
+      },
+      files: {
+        "navigate.js": `window.location.href = "${uri}";`,
+      },
+    };
+
+    testExtension = ExtensionTestUtils.loadExtension(EXTENSION_DATA);
+    await testExtension.startup();
+    return;
+  }
+
+  if (omitTriggeringPrincipal) {
+    // Directly call ContentDispatchChooser without a triggering principal
+    let contentDispatchChooser = Cc[
+      "@mozilla.org/content-dispatch-chooser;1"
+    ].createInstance(Ci.nsIContentDispatchChooser);
+
+    let handler = HandlerServiceTestUtils.getHandlerInfo(scheme);
+
+    contentDispatchChooser.handleURI(
+      handler,
+      Services.io.newURI(uri),
+      null,
+      browser.browsingContext
+    );
+    return;
+  }
+
+  info("Loading uri: " + uri);
+  browser.loadURI(uri, { triggeringPrincipal });
+}
+
+/**
+ * Navigates to a test URL with the given protocol scheme and waits for the
+ * result.
+ * @param {MozBrowser} browser - Browser to navigate.
+ * @param {string} scheme - Scheme of the test url. e.g. irc
+ * @param {Object} [options] - Test options.
+ * @param {Object} [options.permDialogOptions] - Test options for the permission
+ * dialog. If defined, we expect this dialog to be shown.
+ * @param {Object} [options.chooserDialogOptions] - Test options for the chooser
+ * dialog. If defined, we expect this dialog to be shown.
+ * @param {Object} [options.loadOptions] - Options for triggering the protocol
+ * load which causes the dialog to show.
+ * @param {nsIPrincipal} [options.triggeringPrincipal] - Principal to trigger
+ * the load with. Defaults to the browsers content principal.
+ * @returns {Promise} - A promise which resolves once the test is complete.
+ */
+async function testOpenProto(
+  browser,
+  scheme,
+  { permDialogOptions, chooserDialogOptions, loadOptions } = {}
+) {
+  let permDialogOpenPromise;
+  let chooserDialogOpenPromise;
+
+  if (permDialogOptions) {
+    info("Should see permission dialog");
+    permDialogOpenPromise = waitForProtocolPermissionDialog(browser, true);
+  }
+
+  if (chooserDialogOptions) {
+    info("Should see chooser dialog");
+    chooserDialogOpenPromise = waitForProtocolAppChooserDialog(browser, true);
+  }
+  await triggerOpenProto(browser, scheme, loadOptions);
+  let webHandlerLoadedPromise;
+
+  let webHandlerShouldOpen =
+    (!permDialogOptions && !chooserDialogOptions) ||
+    ((permDialogOptions?.actionConfirm || permDialogOptions?.actionChangeApp) &&
+      chooserDialogOptions?.actionConfirm);
+
+  // Register web handler load listener if we expect to trigger it.
+  if (webHandlerShouldOpen) {
+    webHandlerLoadedPromise = waitForHandlerURL(browser, scheme);
+  }
+
+  if (permDialogOpenPromise) {
+    let dialog = await permDialogOpenPromise;
+    let dialogEl = getDialogElementFromSubDialog(dialog);
+    let dialogType = getDialogType(dialog);
+
+    let {
+      hasCheckbox,
+      hasChangeApp,
+      chooserIsNext,
+      actionCheckbox,
+      actionConfirm,
+      actionChangeApp,
+    } = permDialogOptions;
+
+    if (actionChangeApp) {
+      actionConfirm = false;
+    }
+
+    await testCheckbox(dialogEl, dialogType, {
+      hasCheckbox,
+      actionCheckbox,
+    });
+
+    // Check the button label depending on whether we would show the chooser
+    // dialog next or directly open the handler.
+    let acceptBtnLabel = dialogEl.getButton("accept")?.label;
+    if (chooserIsNext) {
+      is(
+        acceptBtnLabel,
+        "Choose Application",
+        "Accept button has choose app label"
+      );
+    } else {
+      is(acceptBtnLabel, "Open Link", "Accept button has open link label");
+    }
+
+    let changeAppLink = dialogEl.ownerDocument.getElementById("change-app");
+    if (typeof hasChangeApp == "boolean") {
+      ok(changeAppLink, "Permission dialog should have changeApp link label");
+      is(
+        !changeAppLink.hidden,
+        hasChangeApp,
+        "Permission dialog change app link label"
+      );
+    }
+
+    if (actionChangeApp) {
+      let dialogClosedPromise = waitForProtocolPermissionDialog(browser, false);
+      changeAppLink.click();
+      await dialogClosedPromise;
+    } else {
+      await closeDialog(browser, dialog, actionConfirm, scheme);
+    }
+  }
+
+  if (chooserDialogOpenPromise) {
+    let dialog = await chooserDialogOpenPromise;
+    let dialogEl = getDialogElementFromSubDialog(dialog);
+    let dialogType = getDialogType(dialog);
+
+    let { hasCheckbox, actionCheckbox, actionConfirm } = chooserDialogOptions;
+
+    await testCheckbox(dialogEl, dialogType, {
+      hasCheckbox,
+      actionCheckbox,
+    });
+
+    await closeDialog(browser, dialog, actionConfirm, scheme);
+  }
+
+  if (webHandlerShouldOpen) {
+    info("Waiting for web handler to open");
+    await webHandlerLoadedPromise;
+  } else {
+    info("Web handler open canceled");
+  }
+
+  // Clean up test extension if needed.
+  await testExtension?.unload();
+}
+
+/**
+ * Inspects the checkbox state and interacts with it.
+ * @param {dialog} dialogEl
+ * @param {string} dialogType - String identifier of dialog type.
+ * Either "permission" or "chooser".
+ * @param {Object} options - Test Options.
+ * @param {boolean} [options.hasCheckbox] - Whether the dialog is expected to
+ * have a visible checkbox.
+ * @param {boolean} [options.hasCheckboxState] - The check state of the checkbox
+ * to test for. true = checked, false = unchecked.
+ * @param {boolean} [options.actionCheckbox] - The state to set on the checkbox.
+ * true = checked, false = unchecked.
+ */
+async function testCheckbox(
+  dialogEl,
+  dialogType,
+  { hasCheckbox, hasCheckboxState = false, actionCheckbox }
+) {
+  let checkbox = dialogEl.ownerDocument.getElementById("remember");
+  if (typeof hasCheckbox == "boolean") {
+    let hiddenEl;
+    if (dialogType == "permission") {
+      hiddenEl = checkbox.parentElement;
+    } else {
+      hiddenEl = checkbox;
+    }
+    is(
+      checkbox && !hiddenEl.hidden,
+      hasCheckbox,
+      "Dialog checkbox has correct visibility."
+    );
+  }
+
+  if (typeof hasCheckboxState == "boolean") {
+    is(checkbox.checked, hasCheckboxState, "Dialog checkbox has correct state");
+  }
+
+  if (typeof actionCheckbox == "boolean") {
+    checkbox.focus();
+    await EventUtils.synthesizeKey("VK_SPACE", undefined, dialogEl.ownerWindow);
+  }
+}
+
+/**
+ * Get the dialog element which is a child of the SubDialogs browser frame.
+ * @param {SubDialog} subDialog - Dialog to get the dialog element for.
+ */
+function getDialogElementFromSubDialog(subDialog) {
+  let dialogEl = subDialog._frame.contentDocument.querySelector("dialog");
+  ok(dialogEl, "SubDialog should have dialog element");
+  return dialogEl;
+}
+
+/**
+ * Wait for the test handler to be opened.
+ * @param {MozBrowser} browser - The browser the load should occur in.
+ * @param {string} scheme - Scheme which triggered the handler to open.
+ */
+function waitForHandlerURL(browser, scheme) {
+  return BrowserTestUtils.browserLoaded(
+    browser,
+    false,
+    url => url == `${ORIGIN1}/?url=${scheme}%3A%2F%2Ftest`
+  );
+}
+
+/**
+ * Test for open-protocol-handler permission.
+ * @param {nsIPrincipal} principal - The principal to test the permission on.
+ * @param {string} scheme - Scheme to generate permission key.
+ * @param {boolean} hasPerm - Whether we expect the princial to set the
+ * permission (true), or not (false).
+ */
+function testPermission(principal, scheme, hasPerm) {
+  let permKey = getSkipProtoDialogPermissionKey(scheme);
+  let result = Services.perms.testPermissionFromPrincipal(principal, permKey);
+  let message = `${permKey} ${hasPerm ? "is" : "is not"} set for ${
+    principal.origin
+  }.`;
+  is(result == Services.perms.ALLOW_ACTION, hasPerm, message);
+}
+
+/**
+ * Get the checkbox element of the dialog used to remember the handler choice or
+ * store the permission.
+ * @param {SubDialog} dialog - Protocol handler dialog embedded in a SubDialog.
+ * @param {string} dialogType - Type of the dialog which holds the checkbox.
+ * @returns {HTMLInputElement} - Checkbox of the dialog.
+ */
+function getDialogCheckbox(dialog, dialogType) {
+  let id;
+  if (dialogType == "permission") {
+    id = "remember-permission";
+  } else {
+    id = "remember";
+  }
+  return dialog._frame.contentDocument.getElementById(id);
+}
+
+function getDialogType(dialog) {
+  let url = dialog._frame.currentURI.spec;
+
+  if (url === DIALOG_URL_PERMISSION) {
+    return "permission";
+  }
+  if (url === DIALOG_URL_APP_CHOOSER) {
+    return "chooser";
+  }
+  throw new Error("Dialog with unexpected url");
+}
+
+/**
+ * Exit a protocol handler SubDialog and wait for it to be fully closed.
+ * @param {MozBrowser} browser - Browser element of the tab where the dialog is
+ * shown.
+ * @param {SubDialog} dialog - SubDialog object which holds the protocol handler
+ * @param {boolean} confirm - Whether to confirm (true) or cancel (false) the
+ * dialog.
+ * @param {string} scheme - The scheme of the protocol the dialog is opened for.
+ * dialog.
+ */
+async function closeDialog(browser, dialog, confirm, scheme) {
+  let dialogClosedPromise = waitForSubDialog(browser, dialog._openedURL, false);
+  let dialogEl = getDialogElementFromSubDialog(dialog);
+
+  if (confirm) {
+    if (getDialogType(dialog) == "chooser") {
+      // Select our test protocol handler
+      let listItem = dialogEl.ownerDocument.querySelector(
+        `richlistitem[name="${scheme}Handler"]`
+      );
+      listItem.click();
+    }
+
+    dialogEl.setAttribute("buttondisabledaccept", false);
+    dialogEl.acceptDialog();
+  } else {
+    dialogEl.cancelDialog();
+  }
+
+  return dialogClosedPromise;
+}
+
+registerCleanupFunction(function() {
+  // Clean up test handlers
+  TEST_PROTOS.forEach(scheme => {
+    let handlerInfo = HandlerServiceTestUtils.getHandlerInfo(scheme);
+    gHandlerService.remove(handlerInfo);
+  });
+
+  // Clear permissions
+  Services.perms.removeAll();
+});
+
+add_task(async function setup() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["security.external_protocol_requires_permission", true]],
+  });
+  initTestHandlers();
+});
+
+/**
+ * Tests that when "remember" is unchecked, we only allow the protocol to be
+ * opened once and don't store any permission.
+ */
+add_task(async function test_permission_allow_once() {
+  for (let scheme of TEST_PROTOS) {
+    await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+      await testOpenProto(browser, scheme, {
+        permDialogOptions: {
+          hasCheckbox: true,
+          hasChangeApp: false,
+          chooserIsNext: true,
+          actionConfirm: true,
+        },
+        chooserDialogOptions: { hasCheckbox: true, actionConfirm: true },
+      });
+    });
+
+    // No permission should be set
+    testPermission(PRINCIPAL1, scheme, false);
+    testPermission(PRINCIPAL2, scheme, false);
+
+    // No preferred app should be set
+    testAlwaysAsk(scheme, true);
+
+    // If we open again we should see the permission dialog
+    await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+      await testOpenProto(browser, scheme, {
+        permDialogOptions: {
+          hasCheckbox: true,
+          hasChangeApp: false,
+          chooserIsNext: true,
+          actionConfirm: false,
+        },
+      });
+    });
+  }
+});
+
+/**
+ * Tests that when checking the "remember" checkbox, the protocol permission
+ * is set correctly and allows the caller to skip the permission dialog in
+ * subsequent calls.
+ */
+add_task(async function test_permission_allow_persist() {
+  for (let [origin, principal] of [
+    [ORIGIN1, PRINCIPAL1],
+    [ORIGIN3, PRINCIPAL3],
+  ]) {
+    for (let scheme of TEST_PROTOS) {
+      info("Testing with origin " + origin);
+      info("testing with principal of origin " + principal.origin);
+      info("testing with protocol " + scheme);
+
+      // Set a permission for an unrelated protocol.
+      // We should still see the permission dialog.
+      Services.perms.addFromPrincipal(
+        principal,
+        getSkipProtoDialogPermissionKey("foobar"),
+        Services.perms.ALLOW_ACTION
+      );
+
+      await BrowserTestUtils.withNewTab(origin, async browser => {
+        await testOpenProto(browser, scheme, {
+          permDialogOptions: {
+            hasCheckbox: true,
+            hasChangeApp: false,
+            chooserIsNext: true,
+            actionCheckbox: true,
+            actionConfirm: true,
+          },
+          chooserDialogOptions: { hasCheckbox: true, actionConfirm: true },
+        });
+      });
+
+      // Permission should be set
+      testPermission(principal, scheme, true);
+      testPermission(PRINCIPAL2, scheme, false);
+
+      // No preferred app should be set
+      testAlwaysAsk(scheme, true);
+
+      // If we open again with the origin where we granted permission, we should
+      // directly get the chooser dialog.
+      await BrowserTestUtils.withNewTab(origin, async browser => {
+        await testOpenProto(browser, scheme, {
+          chooserDialogOptions: {
+            hasCheckbox: true,
+            actionConfirm: false,
+          },
+        });
+      });
+
+      // If we open with the other origin, we should see the permission dialog
+      await BrowserTestUtils.withNewTab(ORIGIN2, async browser => {
+        await testOpenProto(browser, scheme, {
+          permDialogOptions: {
+            hasCheckbox: true,
+            hasChangeApp: false,
+            chooserIsNext: true,
+            actionConfirm: false,
+          },
+        });
+      });
+
+      // Cleanup permissions
+      Services.perms.removeAll();
+    }
+  }
+});
+
+/**
+ * Tests that if a preferred protocol handler is set, the permission dialog
+ * shows the application name and a link which leads to the app chooser.
+ */
+add_task(async function test_permission_application_set() {
+  let scheme = TEST_PROTOS[0];
+  updateAlwaysAsk(scheme, false);
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      permDialogOptions: {
+        hasCheckbox: true,
+        hasChangeApp: true,
+        chooserIsNext: false,
+        actionChangeApp: true,
+      },
+      chooserDialogOptions: { hasCheckbox: true, actionConfirm: true },
+    });
+  });
+
+  // Cleanup
+  updateAlwaysAsk(scheme, true);
+});
+
+/**
+ * Tests that we correctly handle system principals. They should always
+ * skip the permission dialog.
+ */
+add_task(async function test_permission_system_principal() {
+  let scheme = TEST_PROTOS[0];
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      chooserDialogOptions: { hasCheckbox: true, actionConfirm: false },
+      loadOptions: {
+        triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+      },
+    });
+  });
+});
+
+/**
+ * Tests that we don't show the permission dialog if the permission is disabled
+ * by pref.
+ */
+add_task(async function test_permission_disabled() {
+  let scheme = TEST_PROTOS[0];
+
+  await SpecialPowers.pushPrefEnv({
+    set: [["security.external_protocol_requires_permission", false]],
+  });
+
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      chooserDialogOptions: { hasCheckbox: true, actionConfirm: true },
+    });
+  });
+
+  await SpecialPowers.popPrefEnv();
+});
+
+/**
+ * Tests that we directly open the handler if permission and handler are set.
+ */
+add_task(async function test_app_and_permission_set() {
+  let scheme = TEST_PROTOS[1];
+
+  updateAlwaysAsk(scheme, false);
+  Services.perms.addFromPrincipal(
+    PRINCIPAL2,
+    getSkipProtoDialogPermissionKey(scheme),
+    Services.perms.ALLOW_ACTION
+  );
+
+  await BrowserTestUtils.withNewTab(ORIGIN2, async browser => {
+    await testOpenProto(browser, scheme);
+  });
+
+  // Cleanup
+  Services.perms.removeAll();
+  updateAlwaysAsk(scheme, true);
+});
+
+/**
+ * Tests that the alwaysAsk state is not updated if the user cancels the dialog
+ */
+add_task(async function test_change_app_checkbox_cancel() {
+  let scheme = TEST_PROTOS[0];
+
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      permDialogOptions: {
+        hasCheckbox: true,
+        chooserIsNext: true,
+        hasChangeApp: false,
+        actionConfirm: true,
+      },
+      chooserDialogOptions: {
+        hasCheckbox: true,
+        actionCheckbox: true, // Activate checkbox
+        actionConfirm: false, // Cancel dialog
+      },
+    });
+  });
+
+  // Should not have applied value from checkbox
+  testAlwaysAsk(scheme, true);
+});
+
+/**
+ * Tests that the external protocol dialogs behave correctly when a null
+ * principal is passed.
+ */
+add_task(async function test_null_principal() {
+  let scheme = TEST_PROTOS[0];
+
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      loadOptions: {
+        useNullPrincipal: true,
+      },
+      permDialogOptions: {
+        hasCheckbox: false,
+        chooserIsNext: true,
+        hasChangeApp: false,
+        actionConfirm: true,
+      },
+      chooserDialogOptions: {
+        hasCheckbox: true,
+        actionConfirm: false, // Cancel dialog
+      },
+    });
+  });
+});
+
+/**
+ * Tests that the external protocol dialogs behave correctly when no principal
+ * is passed.
+ */
+add_task(async function test_no_principal() {
+  let scheme = TEST_PROTOS[1];
+
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      loadOptions: {
+        omitTriggeringPrincipal: true,
+      },
+      permDialogOptions: {
+        hasCheckbox: false,
+        chooserIsNext: true,
+        hasChangeApp: false,
+        actionConfirm: true,
+      },
+      chooserDialogOptions: {
+        hasCheckbox: true,
+        actionConfirm: false, // Cancel dialog
+      },
+    });
+  });
+});
+
+/**
+ * Tests that we skip the permission dialog for extension callers.
+ */
+add_task(async function test_extension_principal() {
+  let scheme = TEST_PROTOS[0];
+  await BrowserTestUtils.withNewTab(ORIGIN1, async browser => {
+    await testOpenProto(browser, scheme, {
+      loadOptions: {
+        useExtensionPrincipal: true,
+      },
+      chooserDialogOptions: {
+        hasCheckbox: true,
+        actionConfirm: false, // Cancel dialog
+      },
+    });
+  });
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_protocolhandler_loop.js b/uriloader/exthandler/tests/mochitest/browser_protocolhandler_loop.js
new file mode 100644
index 0000000000..b9ba4a7955
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_protocolhandler_loop.js
@@ -0,0 +1,76 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+add_task(async function test_helperapp() {
+  // Set up the test infrastructure:
+  const kProt = "foopydoopydoo";
+  const extProtocolSvc = Cc[
+    "@mozilla.org/uriloader/external-protocol-service;1"
+  ].getService(Ci.nsIExternalProtocolService);
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  let handlerInfo = extProtocolSvc.getProtocolHandlerInfo(kProt);
+  if (handlerSvc.exists(handlerInfo)) {
+    handlerSvc.fillHandlerInfo(handlerInfo, "");
+  }
+  // Say we want to use a specific app:
+  handlerInfo.preferredAction = Ci.nsIHandlerInfo.useHelperApp;
+  handlerInfo.alwaysAskBeforeHandling = false;
+
+  // Say it's us:
+  let selfFile = Services.dirsvc.get("XREExeF", Ci.nsIFile);
+  // Make sure it's the .app
+  if (AppConstants.platform == "macosx") {
+    while (
+      !selfFile.leafName.endsWith(".app") &&
+      !selfFile.leafName.endsWith(".app/")
+    ) {
+      selfFile = selfFile.parent;
+    }
+  }
+  let selfHandlerApp = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  selfHandlerApp.executable = selfFile;
+  handlerInfo.possibleApplicationHandlers.appendElement(selfHandlerApp);
+  handlerInfo.preferredApplicationHandler = selfHandlerApp;
+  handlerSvc.store(handlerInfo);
+
+  await BrowserTestUtils.withNewTab("about:blank", async browser => {
+    // Now, do some safety stubbing. If we do end up recursing we spawn
+    // infinite tabs. We definitely don't want that. Avoid it by stubbing
+    // our external URL handling bits:
+    let oldAddTab = gBrowser.addTab;
+    registerCleanupFunction(
+      () => (gBrowser.addTab = gBrowser.loadOneTab = oldAddTab)
+    );
+    let wrongThingHappenedPromise = new Promise(resolve => {
+      gBrowser.addTab = gBrowser.loadOneTab = function(aURI) {
+        ok(false, "Tried to open unexpected URL in a tab: " + aURI);
+        resolve(null);
+        // Pass a dummy object to avoid upsetting BrowserContentHandler -
+        // if it thinks opening the tab failed, it tries to open a window instead,
+        // which we can't prevent as easily, and at which point we still end up
+        // with runaway tabs.
+        return {};
+      };
+    });
+
+    let askedUserPromise = waitForProtocolAppChooserDialog(browser, true);
+
+    BrowserTestUtils.loadURI(browser, kProt + ":test");
+    let dialog = await Promise.race([
+      wrongThingHappenedPromise,
+      askedUserPromise,
+    ]);
+    ok(dialog, "Should have gotten a dialog");
+
+    let closePromise = waitForProtocolAppChooserDialog(browser, false);
+    dialog.close();
+    await closePromise;
+    askedUserPromise = null;
+  });
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_remember_download_option.js b/uriloader/exthandler/tests/mochitest/browser_remember_download_option.js
new file mode 100644
index 0000000000..28bd50a120
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_remember_download_option.js
@@ -0,0 +1,61 @@
+add_task(async function() {
+  // create mocked objects
+  let launcher = createMockedObjects(true);
+
+  // open helper app dialog with mocked launcher
+  let dlg = await openHelperAppDialog(launcher);
+
+  let doc = dlg.document;
+  let dialogElement = doc.getElementById("unknownContentType");
+
+  // Set remember choice
+  ok(
+    !doc.getElementById("rememberChoice").checked,
+    "Remember choice checkbox should be not checked."
+  );
+  doc.getElementById("rememberChoice").checked = true;
+
+  // Make sure the mock handler information is not in nsIHandlerService
+  ok(
+    !gHandlerSvc.exists(launcher.MIMEInfo),
+    "Should not be in nsIHandlerService."
+  );
+
+  // close the dialog by pushing the ok button.
+  let dialogClosedPromise = BrowserTestUtils.windowClosed(dlg);
+  // Make sure the ok button is enabled, since the ok button might be disabled by
+  // EnableDelayHelper mechanism. Please refer the detailed
+  // https://searchfox.org/mozilla-central/source/toolkit/components/prompts/src/SharedPromptUtils.jsm#53
+  dialogElement.getButton("accept").disabled = false;
+  dialogElement.acceptDialog();
+  await dialogClosedPromise;
+
+  // check the mocked handler information is saved in nsIHandlerService
+  ok(gHandlerSvc.exists(launcher.MIMEInfo), "Should be in nsIHandlerService.");
+  // check the extension.
+  var mimeType = gHandlerSvc.getTypeFromExtension("abc");
+  is(mimeType, launcher.MIMEInfo.type, "Got correct mime type.");
+  for (let handlerInfo of gHandlerSvc.enumerate()) {
+    if (handlerInfo.type == launcher.MIMEInfo.type) {
+      // check the alwaysAskBeforeHandling
+      ok(
+        !handlerInfo.alwaysAskBeforeHandling,
+        "Should turn off the always ask."
+      );
+      // check the preferredApplicationHandler
+      ok(
+        handlerInfo.preferredApplicationHandler.equals(
+          launcher.MIMEInfo.preferredApplicationHandler
+        ),
+        "Should be equal to the mockedHandlerApp."
+      );
+      // check the perferredAction
+      is(
+        handlerInfo.preferredAction,
+        launcher.MIMEInfo.preferredAction,
+        "Should be equal to Ci.nsIHandlerInfo.useHelperApp."
+      );
+      break;
+    }
+  }
+});
diff --git a/uriloader/exthandler/tests/mochitest/browser_web_protocol_handlers.js b/uriloader/exthandler/tests/mochitest/browser_web_protocol_handlers.js
new file mode 100644
index 0000000000..66f461834c
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_web_protocol_handlers.js
@@ -0,0 +1,124 @@
+let testURL =
+  "https://example.com/browser/" +
+  "uriloader/exthandler/tests/mochitest/protocolHandler.html";
+
+add_task(async function() {
+  await SpecialPowers.pushPrefEnv({
+    set: [["security.external_protocol_requires_permission", false]],
+  });
+
+  // Load a page registering a protocol handler.
+  let browser = gBrowser.selectedBrowser;
+  BrowserTestUtils.loadURI(browser, testURL);
+  await BrowserTestUtils.browserLoaded(browser, false, testURL);
+
+  // Register the protocol handler by clicking the notificationbar button.
+  let notificationValue = "Protocol Registration: web+testprotocol";
+  let getNotification = () =>
+    gBrowser.getNotificationBox().getNotificationWithValue(notificationValue);
+  await BrowserTestUtils.waitForCondition(getNotification);
+  let notification = getNotification();
+  let button = notification.querySelector("button");
+  ok(button, "got registration button");
+  button.click();
+
+  // Set the new handler as default.
+  const protoSvc = Cc[
+    "@mozilla.org/uriloader/external-protocol-service;1"
+  ].getService(Ci.nsIExternalProtocolService);
+  let protoInfo = protoSvc.getProtocolHandlerInfo("web+testprotocol");
+  is(
+    protoInfo.preferredAction,
+    protoInfo.useHelperApp,
+    "using a helper application is the preferred action"
+  );
+  ok(!protoInfo.preferredApplicationHandler, "no preferred handler is set");
+  let handlers = protoInfo.possibleApplicationHandlers;
+  is(1, handlers.length, "only one handler registered for web+testprotocol");
+  let handler = handlers.queryElementAt(0, Ci.nsIHandlerApp);
+  ok(handler instanceof Ci.nsIWebHandlerApp, "the handler is a web handler");
+  is(
+    handler.uriTemplate,
+    "https://example.com/foobar?uri=%s",
+    "correct url template"
+  );
+  protoInfo.preferredApplicationHandler = handler;
+  protoInfo.alwaysAskBeforeHandling = false;
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+  handlerSvc.store(protoInfo);
+
+  const expectedURL =
+    "https://example.com/foobar?uri=web%2Btestprotocol%3Atest";
+
+  // Create a framed link:
+  await SpecialPowers.spawn(browser, [], async function() {
+    let iframe = content.document.createElement("iframe");
+    iframe.src = `data:text/html,<a href="web+testprotocol:test">Click me</a>`;
+    content.document.body.append(iframe);
+    // Can't return this promise because it resolves to the event object.
+    await ContentTaskUtils.waitForEvent(iframe, "load");
+    iframe.contentDocument.querySelector("a").click();
+  });
+  let kidContext = browser.browsingContext.children[0];
+  await TestUtils.waitForCondition(() => {
+    let spec = kidContext.currentWindowGlobal?.documentURI?.spec || "";
+    return spec == expectedURL;
+  });
+  is(
+    kidContext.currentWindowGlobal.documentURI.spec,
+    expectedURL,
+    "Should load in frame."
+  );
+
+  // Middle-click a testprotocol link and check the new tab is correct
+  let link = "#link";
+
+  let promiseTabOpened = BrowserTestUtils.waitForNewTab(gBrowser, expectedURL);
+  await BrowserTestUtils.synthesizeMouseAtCenter(link, { button: 1 }, browser);
+  let tab = await promiseTabOpened;
+  gBrowser.selectedTab = tab;
+  is(
+    gURLBar.value,
+    expectedURL,
+    "the expected URL is displayed in the location bar"
+  );
+  BrowserTestUtils.removeTab(tab);
+
+  // Shift-click the testprotocol link and check the new window.
+  let newWindowPromise = BrowserTestUtils.waitForNewWindow({
+    url: expectedURL,
+  });
+  await BrowserTestUtils.synthesizeMouseAtCenter(
+    link,
+    { shiftKey: true },
+    browser
+  );
+  let win = await newWindowPromise;
+  await BrowserTestUtils.waitForCondition(
+    () => win.gBrowser.currentURI.spec == expectedURL
+  );
+  is(
+    win.gURLBar.value,
+    expectedURL,
+    "the expected URL is displayed in the location bar"
+  );
+  await BrowserTestUtils.closeWindow(win);
+
+  // Click the testprotocol link and check the url in the current tab.
+  let loadPromise = BrowserTestUtils.browserLoaded(browser);
+  await BrowserTestUtils.synthesizeMouseAtCenter(link, {}, browser);
+  await loadPromise;
+  await BrowserTestUtils.waitForCondition(() => gURLBar.value != testURL);
+  is(
+    gURLBar.value,
+    expectedURL,
+    "the expected URL is displayed in the location bar"
+  );
+
+  // Cleanup.
+  protoInfo.preferredApplicationHandler = null;
+  handlers.removeElementAt(0);
+  handlerSvc.store(protoInfo);
+});
diff --git a/uriloader/exthandler/tests/mochitest/download.bin b/uriloader/exthandler/tests/mochitest/download.bin
new file mode 100644
index 0000000000..0e4b0c7bae
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/download.bin
@@ -0,0 +1 @@
+abc123
diff --git a/uriloader/exthandler/tests/mochitest/download.sjs b/uriloader/exthandler/tests/mochitest/download.sjs
new file mode 100644
index 0000000000..bee7bd7015
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/download.sjs
@@ -0,0 +1,38 @@
+"use strict";
+
+Cu.import("resource://gre/modules/Timer.jsm");
+
+function actuallyHandleRequest(req, res) {
+  res.setHeader("Content-Type", "application/octet-stream", false);
+  res.write("abc123");
+  res.finish();
+}
+
+function handleRequest(req, res) {
+  if (req.queryString.includes('finish')) {
+    res.write("OK");
+    let downloadReq = null;
+    getObjectState("downloadReq", o => { downloadReq = o });
+    // Two possibilities: either the download request has already reached us, or not.
+    if (downloadReq) {
+      downloadReq.wrappedJSObject.callback();
+    } else {
+      // Set a variable to allow the request to complete immediately:
+      setState("finishReq", "true");
+    }
+  } else if (req.queryString.includes('reset')) {
+    res.write("OK");
+    setObjectState("downloadReq", null);
+    setState("finishReq", "false");
+  } else {
+    res.processAsync();
+    if (getState("finishReq") === "true") {
+      actuallyHandleRequest(req, res);
+    } else {
+      let o = {callback() { actuallyHandleRequest(req, res) }};
+      o.wrappedJSObject = o;
+      o.QueryInterface = () => o;
+      setObjectState("downloadReq", o);
+    }
+  }
+}
diff --git a/uriloader/exthandler/tests/mochitest/download_page.html b/uriloader/exthandler/tests/mochitest/download_page.html
new file mode 100644
index 0000000000..5a264888fa
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/download_page.html
@@ -0,0 +1,22 @@
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE html>
+<html>
+<head>
+  <meta charset=UTF-8>
+  <title>Test page for link clicking</title>
+  <script type="text/javascript">
+    function launch_download(extra) {
+      window.open("download.sjs", "_blank", "height=100,width=100" + extra);
+    }
+  </script>
+</head>
+<body>
+  <a href="download.bin" id="regular_load">regular load</a>
+  <a href="download.bin" id="target_blank" target="_blank" rel="opener">target blank</a>
+  <a href="#" onclick="launch_download(''); return false" id="new_window">new window</a>
+  <a href="#" onclick="window.open('download_page.html?newwin'); return false" id="open_in_new_tab">click to reopen</a>
+  <a href="download.bin" id="target_blank_no_opener" rel="noopener" target="_blank">target blank (noopener)</a>
+  <a href="#" onclick="window.open('download.bin', '_blank', 'noopener'); return false" id="open_in_new_tab_no_opener">click to reopen (noopener)</a>
+  <a href="#" onclick="launch_download(',noopener'); return false" id="new_window_no_opener">new window (noopener)</a>
+</body>
diff --git a/uriloader/exthandler/tests/mochitest/file_as.exe b/uriloader/exthandler/tests/mochitest/file_as.exe
new file mode 100644
index 0000000000..f2f5ab47f3
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_as.exe
@@ -0,0 +1 @@
+Not actually an executable... but let's pretend!
diff --git a/uriloader/exthandler/tests/mochitest/file_as.exe^headers^ b/uriloader/exthandler/tests/mochitest/file_as.exe^headers^
new file mode 100644
index 0000000000..89f22e30be
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_as.exe^headers^
@@ -0,0 +1,2 @@
+Content-Type: binary/octet-stream
+Content-Disposition: attachment
diff --git a/uriloader/exthandler/tests/mochitest/file_external_protocol_iframe.html b/uriloader/exthandler/tests/mochitest/file_external_protocol_iframe.html
new file mode 100644
index 0000000000..eb2fb74441
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_external_protocol_iframe.html
@@ -0,0 +1 @@
+<iframe src="mailto:foo@bar.com"></iframe>
diff --git a/uriloader/exthandler/tests/mochitest/file_nested_protocol_request.html b/uriloader/exthandler/tests/mochitest/file_nested_protocol_request.html
new file mode 100644
index 0000000000..b1bb863f89
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_nested_protocol_request.html
@@ -0,0 +1 @@
+<iframe srcdoc="<a href='mailto:help@example.com'>Mail someone</a>"></iframe>
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf b/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf^headers^ b/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf^headers^
new file mode 100644
index 0000000000..d1d59b9754
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_application_pdf.pdf^headers^
@@ -0,0 +1,2 @@
+content-disposition: attachment; filename=file_pdf_application_pdf.pdf; filename*=UTF-8''file_pdf_application_pdf.pdf
+content-type: application/pdf
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf b/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf^headers^ b/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf^headers^
new file mode 100644
index 0000000000..157c0e0943
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_application_unknown.pdf^headers^
@@ -0,0 +1,2 @@
+content-disposition: attachment; filename=file_pdf_application_unknown.pdf; filename*=UTF-8''file_pdf_application_unknown.pdf
+content-type: application/unknown
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf b/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf
diff --git a/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf^headers^ b/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf^headers^
new file mode 100644
index 0000000000..6358f54f48
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_pdf_binary_octet_stream.pdf^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: attachment; filename="file_pdf_binary_octet_stream.pdf"; filename*=UTF-8''file_pdf_binary_octet_stream.pdf
+Content-Type: binary/octet-stream
diff --git a/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt b/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt
diff --git a/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt^headers^ b/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt^headers^
new file mode 100644
index 0000000000..37823166a4
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_txt_attachment_test.txt^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: attachment; filename=file_text_attachment_test.txt
+Content-Type: text/plain
diff --git a/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png b/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png
new file mode 100644
index 0000000000..743292dc6f
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png
diff --git a/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png^headers^ b/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png^headers^
new file mode 100644
index 0000000000..06e0cd957f
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_with@@funny_name.png^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: inline; filename=file_with%40%40funny_name.png
+Content-Type: image/png
diff --git a/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm b/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm
new file mode 100644
index 0000000000..7bc738b8b4
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm
diff --git a/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm^headers^ b/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm^headers^
new file mode 100644
index 0000000000..b77e9d3687
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_with[funny_name.webm^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: inline; filename=file_with%5Bfunny_name.webm
+Content-Type: video/webm
diff --git a/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml b/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml
new file mode 100644
index 0000000000..3a5792586a
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml
@@ -0,0 +1,4 @@
+<?xml version = "1.0" encoding = "utf-8"?>
+
+<something>
+</something>
diff --git a/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml^headers^ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml^headers^
new file mode 100644
index 0000000000..5bdc4448e8
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_binary_octet_stream.xml^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: attachment
+Content-Type: binary/octet-stream
diff --git a/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml b/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml
new file mode 100644
index 0000000000..3a5792586a
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml
@@ -0,0 +1,4 @@
+<?xml version = "1.0" encoding = "utf-8"?>
+
+<something>
+</something>
diff --git a/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml^headers^ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml^headers^
new file mode 100644
index 0000000000..ac0355d976
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/file_xml_attachment_test.xml^headers^
@@ -0,0 +1,2 @@
+Content-Disposition: attachment; filename=file_xml_attachment_test.xml
+Content-Type: text/xml
diff --git a/uriloader/exthandler/tests/mochitest/handlerApp.xhtml b/uriloader/exthandler/tests/mochitest/handlerApp.xhtml
new file mode 100644
index 0000000000..e519e80029
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/handlerApp.xhtml
@@ -0,0 +1,28 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Pseudo Web Handler App</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body onload="onLoad()">
+Pseudo Web Handler App
+
+<script class="testbody" type="text/javascript">
+<![CDATA[
+function onLoad() {
+  // if we have a window.opener, this must be the windowContext
+  // instance of this test.  check that we got the URI right and clean up.
+  if (window.opener) {
+    window.opener.is(location.search,
+                     "?uri=" + encodeURIComponent(window.opener.testURI),
+                     "uri passed to web-handler app");
+    window.opener.SimpleTest.finish();
+  }
+
+  window.close();
+}
+]]>
+</script>
+
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/handlerApps.js b/uriloader/exthandler/tests/mochitest/handlerApps.js
new file mode 100644
index 0000000000..aa841f13be
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/handlerApps.js
@@ -0,0 +1,118 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// handlerApp.xhtml grabs this for verification purposes via window.opener
+var testURI = "webcal://127.0.0.1/rheeeeet.html";
+
+const Cc = SpecialPowers.Cc;
+
+function test() {
+  // set up the web handler object
+  var webHandler = Cc[
+    "@mozilla.org/uriloader/web-handler-app;1"
+  ].createInstance(SpecialPowers.Ci.nsIWebHandlerApp);
+  webHandler.name = "Test Web Handler App";
+  webHandler.uriTemplate =
+    "https://example.com/tests/uriloader/exthandler/tests/mochitest/" +
+    "handlerApp.xhtml?uri=%s";
+
+  // set up the uri to test with
+  /* eslint-disable mozilla/use-services */
+
+  var ioService = Cc["@mozilla.org/network/io-service;1"].getService(
+    SpecialPowers.Ci.nsIIOService
+  );
+
+  var uri = ioService.newURI(testURI);
+
+  // create a window, and launch the handler in it
+  var newWindow = window.open("", "handlerWindow", "height=300,width=300");
+  var windowContext = SpecialPowers.wrap(newWindow).docShell;
+
+  webHandler.launchWithURI(uri, windowContext);
+
+  // if we get this far without an exception, we've at least partly passed
+  // (remaining check in handlerApp.xhtml)
+  ok(true, "webHandler launchWithURI (existing window/tab) started");
+
+  // make the web browser launch in its own window/tab
+  webHandler.launchWithURI(uri);
+
+  // if we get this far without an exception, we've passed
+  ok(true, "webHandler launchWithURI (new window/tab) test started");
+
+  // set up the local handler object
+  var localHandler = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(SpecialPowers.Ci.nsILocalHandlerApp);
+  localHandler.name = "Test Local Handler App";
+
+  // get a local app that we know will be there and do something sane
+  /* eslint-disable mozilla/use-services */
+
+  var osString = Cc["@mozilla.org/xre/app-info;1"].getService(
+    SpecialPowers.Ci.nsIXULRuntime
+  ).OS;
+
+  var dirSvc = Cc["@mozilla.org/file/directory_service;1"].getService(
+    SpecialPowers.Ci.nsIDirectoryServiceProvider
+  );
+  if (osString == "WINNT") {
+    var windowsDir = dirSvc.getFile("WinD", {});
+    var exe = windowsDir.clone().QueryInterface(SpecialPowers.Ci.nsIFile);
+    exe.appendRelativePath("SYSTEM32\\HOSTNAME.EXE");
+  } else if (osString == "Darwin") {
+    var localAppsDir = dirSvc.getFile("LocApp", {});
+    exe = localAppsDir.clone();
+    exe.append("iCal.app"); // lingers after the tests finish, but this seems
+    // seems better than explicitly killing it, since
+    // developers who run the tests locally may well
+    // information in their running copy of iCal
+
+    if (navigator.userAgent.match(/ SeaMonkey\//)) {
+      // SeaMonkey tinderboxes don't like to have iCal lingering (and focused)
+      // on next test suite run(s).
+      todo(false, "On SeaMonkey, testing OS X as generic Unix. (Bug 749872)");
+
+      // assume a generic UNIX variant
+      exe = Cc["@mozilla.org/file/local;1"].createInstance(
+        SpecialPowers.Ci.nsIFile
+      );
+      exe.initWithPath("/bin/echo");
+    }
+  } else {
+    // assume a generic UNIX variant
+    exe = Cc["@mozilla.org/file/local;1"].createInstance(
+      SpecialPowers.Ci.nsIFile
+    );
+    exe.initWithPath("/bin/echo");
+  }
+
+  localHandler.executable = exe;
+  localHandler.launchWithURI(ioService.newURI(testURI));
+
+  // if we get this far without an exception, we've passed
+  ok(true, "localHandler launchWithURI test");
+
+  // if we ever decide that killing iCal is the right thing to do, change
+  // the if statement below from "NOTDarwin" to "Darwin"
+  if (osString == "NOTDarwin") {
+    var killall = Cc["@mozilla.org/file/local;1"].createInstance(
+      SpecialPowers.Ci.nsIFile
+    );
+    killall.initWithPath("/usr/bin/killall");
+
+    var process = Cc["@mozilla.org/process/util;1"].createInstance(
+      SpecialPowers.Ci.nsIProcess
+    );
+    process.init(killall);
+
+    var args = ["iCal"];
+    process.run(false, args, args.length);
+  }
+
+  SimpleTest.waitForExplicitFinish();
+}
+
+test();
diff --git a/uriloader/exthandler/tests/mochitest/head.js b/uriloader/exthandler/tests/mochitest/head.js
new file mode 100644
index 0000000000..3b0d8a4072
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/head.js
@@ -0,0 +1,277 @@
+var { FileUtils } = ChromeUtils.import("resource://gre/modules/FileUtils.jsm");
+var { HandlerServiceTestUtils } = ChromeUtils.import(
+  "resource://testing-common/HandlerServiceTestUtils.jsm"
+);
+
+var gMimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+var gHandlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+  Ci.nsIHandlerService
+);
+
+function createMockedHandlerApp() {
+  // Mock the executable
+  let mockedExecutable = FileUtils.getFile("TmpD", ["mockedExecutable"]);
+  if (!mockedExecutable.exists()) {
+    mockedExecutable.create(Ci.nsIFile.NORMAL_FILE_TYPE, 0o755);
+  }
+
+  // Mock the handler app
+  let mockedHandlerApp = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  mockedHandlerApp.executable = mockedExecutable;
+  mockedHandlerApp.detailedDescription = "Mocked handler app";
+
+  registerCleanupFunction(function() {
+    // remove the mocked executable from disk.
+    if (mockedExecutable.exists()) {
+      mockedExecutable.remove(true);
+    }
+  });
+
+  return mockedHandlerApp;
+}
+
+function createMockedObjects(createHandlerApp) {
+  // Mock the mime info
+  let internalMockedMIME = gMimeSvc.getFromTypeAndExtension(
+    "text/x-test-handler",
+    null
+  );
+  internalMockedMIME.alwaysAskBeforeHandling = true;
+  internalMockedMIME.preferredAction = Ci.nsIHandlerInfo.useHelperApp;
+  internalMockedMIME.appendExtension("abc");
+  if (createHandlerApp) {
+    let mockedHandlerApp = createMockedHandlerApp();
+    internalMockedMIME.description = mockedHandlerApp.detailedDescription;
+    internalMockedMIME.possibleApplicationHandlers.appendElement(
+      mockedHandlerApp
+    );
+    internalMockedMIME.preferredApplicationHandler = mockedHandlerApp;
+  }
+
+  // Proxy for the mocked MIME info for faking the read-only attributes
+  let mockedMIME = new Proxy(internalMockedMIME, {
+    get(target, property) {
+      switch (property) {
+        case "hasDefaultHandler":
+          return true;
+        case "defaultDescription":
+          return "Default description";
+        default:
+          return target[property];
+      }
+    },
+  });
+
+  // Mock the launcher:
+  let mockedLauncher = {
+    MIMEInfo: mockedMIME,
+    source: Services.io.newURI("http://www.mozilla.org/"),
+    suggestedFileName: "test_download_dialog.abc",
+    targetFileIsExecutable: false,
+    saveToDisk() {},
+    cancel() {},
+    launchWithApplication() {},
+    setWebProgressListener() {},
+    saveDestinationAvailable() {},
+    contentLength: 42,
+    targetFile: null, // never read
+    // PRTime is microseconds since epoch, Date.now() returns milliseconds:
+    timeDownloadStarted: Date.now() * 1000,
+    QueryInterface: ChromeUtils.generateQI([
+      "nsICancelable",
+      "nsIHelperAppLauncher",
+    ]),
+  };
+
+  registerCleanupFunction(function() {
+    // remove the mocked mime info from database.
+    let mockHandlerInfo = gMimeSvc.getFromTypeAndExtension(
+      "text/x-test-handler",
+      null
+    );
+    if (gHandlerSvc.exists(mockHandlerInfo)) {
+      gHandlerSvc.remove(mockHandlerInfo);
+    }
+  });
+
+  return mockedLauncher;
+}
+
+async function openHelperAppDialog(launcher) {
+  let helperAppDialog = Cc[
+    "@mozilla.org/helperapplauncherdialog;1"
+  ].createInstance(Ci.nsIHelperAppLauncherDialog);
+
+  let helperAppDialogShownPromise = BrowserTestUtils.domWindowOpenedAndLoaded();
+  try {
+    helperAppDialog.show(launcher, window, "foopy");
+  } catch (ex) {
+    ok(
+      false,
+      "Trying to show unknownContentType.xhtml failed with exception: " + ex
+    );
+    Cu.reportError(ex);
+  }
+  let dlg = await helperAppDialogShownPromise;
+
+  is(
+    dlg.location.href,
+    "chrome://mozapps/content/downloads/unknownContentType.xhtml",
+    "Got correct dialog"
+  );
+
+  return dlg;
+}
+
+async function waitForSubDialog(browser, url, state) {
+  let eventStr = state ? "dialogopen" : "dialogclose";
+
+  let tabDialogBox = gBrowser.getTabDialogBox(browser);
+  let dialogStack = tabDialogBox.getTabDialogManager()._dialogStack;
+
+  let checkFn;
+
+  if (state) {
+    checkFn = dialogEvent => dialogEvent.detail.dialog?._openedURL == url;
+  }
+
+  let event = await BrowserTestUtils.waitForEvent(
+    dialogStack,
+    eventStr,
+    true,
+    checkFn
+  );
+
+  let { dialog } = event.detail;
+
+  // If the dialog is closing wait for it to be fully closed before resolving
+  if (!state) {
+    await dialog._closingPromise;
+  }
+
+  return event.detail.dialog;
+}
+
+/**
+ * Wait for protocol permission dialog open/close.
+ * @param {MozBrowser} browser - Browser element the dialog belongs to.
+ * @param {boolean} state - true: dialog open, false: dialog close
+ * @returns {Promise<SubDialog>} - Returns a promise which resolves with the
+ * SubDialog object of the dialog which closed or opened.
+ */
+async function waitForProtocolPermissionDialog(browser, state) {
+  return waitForSubDialog(
+    browser,
+    "chrome://mozapps/content/handling/permissionDialog.xhtml",
+    state
+  );
+}
+
+/**
+ * Wait for protocol app chooser dialog open/close.
+ * @param {MozBrowser} browser - Browser element the dialog belongs to.
+ * @param {boolean} state - true: dialog open, false: dialog close
+ * @returns {Promise<SubDialog>} - Returns a promise which resolves with the
+ * SubDialog object of the dialog which closed or opened.
+ */
+async function waitForProtocolAppChooserDialog(browser, state) {
+  return waitForSubDialog(
+    browser,
+    "chrome://mozapps/content/handling/appChooser.xhtml",
+    state
+  );
+}
+
+async function promiseDownloadFinished(list) {
+  return new Promise(resolve => {
+    list.addView({
+      onDownloadChanged(download) {
+        info("Download changed!");
+        if (download.succeeded || download.error) {
+          info("Download succeeded or errored");
+          list.removeView(this);
+          resolve(download);
+        }
+      },
+    });
+  });
+}
+
+function setupMailHandler() {
+  let mailHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("mailto");
+  let gOldMailHandlers = [];
+
+  // Remove extant web handlers because they have icons that
+  // we fetch from the web, which isn't allowed in tests.
+  let handlers = mailHandlerInfo.possibleApplicationHandlers;
+  for (let i = handlers.Count() - 1; i >= 0; i--) {
+    try {
+      let handler = handlers.queryElementAt(i, Ci.nsIWebHandlerApp);
+      gOldMailHandlers.push(handler);
+      // If we get here, this is a web handler app. Remove it:
+      handlers.removeElementAt(i);
+    } catch (ex) {}
+  }
+
+  let previousHandling = mailHandlerInfo.alwaysAskBeforeHandling;
+  mailHandlerInfo.alwaysAskBeforeHandling = true;
+
+  // Create a dummy web mail handler so we always know the mailto: protocol.
+  // Without this, the test fails on VMs without a default mailto: handler,
+  // because no dialog is ever shown, as we ignore subframe navigations to
+  // protocols that cannot be handled.
+  let dummy = Cc["@mozilla.org/uriloader/web-handler-app;1"].createInstance(
+    Ci.nsIWebHandlerApp
+  );
+  dummy.name = "Handler 1";
+  dummy.uriTemplate = "https://example.com/first/%s";
+  mailHandlerInfo.possibleApplicationHandlers.appendElement(dummy);
+
+  gHandlerSvc.store(mailHandlerInfo);
+  registerCleanupFunction(() => {
+    // Re-add the original protocol handlers:
+    let mailHandlers = mailHandlerInfo.possibleApplicationHandlers;
+    for (let i = handlers.Count() - 1; i >= 0; i--) {
+      try {
+        // See if this is a web handler. If it is, it'll throw, otherwise,
+        // we will remove it.
+        mailHandlers.queryElementAt(i, Ci.nsIWebHandlerApp);
+        mailHandlers.removeElementAt(i);
+      } catch (ex) {}
+    }
+    for (let h of gOldMailHandlers) {
+      mailHandlers.appendElement(h);
+    }
+    mailHandlerInfo.alwaysAskBeforeHandling = previousHandling;
+    gHandlerSvc.store(mailHandlerInfo);
+  });
+}
+
+let gDownloadDir;
+
+async function setDownloadDir() {
+  let tmpDir = await PathUtils.getTempDir();
+  tmpDir = PathUtils.join(
+    tmpDir,
+    "testsavedir" + Math.floor(Math.random() * 2 ** 32)
+  );
+  // Create this dir if it doesn't exist (ignores existing dirs)
+  await IOUtils.makeDirectory(tmpDir);
+  registerCleanupFunction(async function() {
+    try {
+      await IOUtils.remove(tmpDir, { recursive: true });
+    } catch (e) {
+      Cu.reportError(e);
+    }
+  });
+  Services.prefs.setIntPref("browser.download.folderList", 2);
+  Services.prefs.setCharPref("browser.download.dir", tmpDir);
+  return tmpDir;
+}
+
+add_task(async function test_common_initialize() {
+  gDownloadDir = await setDownloadDir();
+  Services.prefs.setCharPref("browser.download.loglevel", "Debug");
+});
diff --git a/uriloader/exthandler/tests/mochitest/invalidCharFileExtension.sjs b/uriloader/exthandler/tests/mochitest/invalidCharFileExtension.sjs
new file mode 100644
index 0000000000..d12e2904d9
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/invalidCharFileExtension.sjs
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function handleRequest(request, response) {
+  response.setStatusLine(request.httpVersion, 200, "OK");
+
+  if (!request.queryString.match(/^name=/))
+    return;
+  var name = decodeURIComponent(request.queryString.substring(5));
+
+  response.setHeader("Content-Type", "image/png; name=\"" + name + "\"");
+  response.setHeader("Content-Disposition", "attachment; filename=\"" + name + "\"");
+}
diff --git a/uriloader/exthandler/tests/mochitest/mochitest.ini b/uriloader/exthandler/tests/mochitest/mochitest.ini
new file mode 100644
index 0000000000..be3b6bb37e
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/mochitest.ini
@@ -0,0 +1,23 @@
+[DEFAULT]
+support-files =
+  handlerApp.xhtml
+  handlerApps.js
+
+[test_handlerApps.xhtml]
+skip-if = (toolkit == 'android' || os == 'mac') || e10s # OS X: bug 786938
+scheme = https
+[test_invalidCharFileExtension.xhtml]
+skip-if = toolkit == 'android' && !is_fennec # Bug 1525959
+support-files =
+  HelperAppLauncherDialog_chromeScript.js
+  invalidCharFileExtension.sjs
+[test_nullCharFile.xhtml]
+skip-if = toolkit == 'android' && !is_fennec # Bug 1525959
+support-files =
+  HelperAppLauncherDialog_chromeScript.js
+[test_unknown_ext_protocol_handlers.html]
+[test_unsafeBidiChars.xhtml]
+skip-if = toolkit == 'android' && !is_fennec # Bug 1525959
+support-files =
+  HelperAppLauncherDialog_chromeScript.js
+  unsafeBidiFileName.sjs
diff --git a/uriloader/exthandler/tests/mochitest/protocolHandler.html b/uriloader/exthandler/tests/mochitest/protocolHandler.html
new file mode 100644
index 0000000000..eff8a53aab
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/protocolHandler.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Protocol handler</title>
+    <meta content="text/html;charset=utf-8" http-equiv="Content-Type">
+    <meta content="utf-8" http-equiv="encoding">
+  </head>
+  <body>
+    <script type="text/javascript">
+      navigator.registerProtocolHandler("web+testprotocol",
+          "https://example.com/foobar?uri=%s",
+          "Test Protocol");
+    </script>
+    <a id="link" href="web+testprotocol:test">testprotocol link</a>
+  </body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/test_handlerApps.xhtml b/uriloader/exthandler/tests/mochitest/test_handlerApps.xhtml
new file mode 100644
index 0000000000..d6166fd270
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/test_handlerApps.xhtml
@@ -0,0 +1,11 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Test for Handler Apps </title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="handlerApps.js"/>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/test_invalidCharFileExtension.xhtml b/uriloader/exthandler/tests/mochitest/test_invalidCharFileExtension.xhtml
new file mode 100644
index 0000000000..4ee1a6a1c1
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/test_invalidCharFileExtension.xhtml
@@ -0,0 +1,47 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Test for Handling of unsafe bidi chars</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<iframe id="test"></iframe>
+<script type="text/javascript">
+var tests = [
+  ["test.png:large", "test.png"],
+  ["test.png/large", "test.png"],
+  [":test.png::large:", "test.png"],
+];
+
+add_task(async function() {
+  let url = SimpleTest.getTestFileURL("HelperAppLauncherDialog_chromeScript.js");
+  let chromeScript = SpecialPowers.loadChromeScript(url);
+
+  for (let [name, expected] of tests) {
+    let promiseName = new Promise(function(resolve) {
+      chromeScript.addMessageListener("suggestedFileName",
+                                      function listener(data) {
+        chromeScript.removeMessageListener("suggestedFileName", listener);
+        resolve(data);
+      });
+    });
+    document.getElementById("test").src =
+      "invalidCharFileExtension.sjs?name=" + encodeURIComponent(name);
+    is((await promiseName), expected, "got the expected sanitized name");
+  }
+
+  let promise = new Promise(function(resolve) {
+    chromeScript.addMessageListener("unregistered", function listener() {
+      chromeScript.removeMessageListener("unregistered", listener);
+      resolve();
+    });
+  });
+  chromeScript.sendAsyncMessage("unregister");
+  await promise;
+
+  chromeScript.destroy();
+});
+</script>
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/test_nullCharFile.xhtml b/uriloader/exthandler/tests/mochitest/test_nullCharFile.xhtml
new file mode 100644
index 0000000000..9bb1140718
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/test_nullCharFile.xhtml
@@ -0,0 +1,49 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Test for Handling of null char</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<iframe id="test"></iframe>
+<script type="text/javascript">
+var tests = [
+  ["test.html\u0000.png", "test.html_.png"],
+  ["test.html.\u0000png", "test.html._png"],
+];
+
+add_task(async function() {
+  let url = SimpleTest.getTestFileURL("HelperAppLauncherDialog_chromeScript.js");
+  let chromeScript = SpecialPowers.loadChromeScript(url);
+
+  for (let [name, expected] of tests) {
+    let promiseName = new Promise(function(resolve) {
+      chromeScript.addMessageListener("suggestedFileName",
+                                      function listener(data) {
+        chromeScript.removeMessageListener("suggestedFileName", listener);
+        resolve(data);
+      });
+    });
+    const a = document.createElement('a');
+    // Pass an unknown mimetype so we don't "correct" the extension:
+    a.href = "data:application/baconizer;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAAAAAA6fptVAAAACklEQVQI12NgAAAAAgAB4iG8MwAAAABJRU5ErkJggg==";
+    a.download = name;
+    a.dispatchEvent(new MouseEvent('click'));
+    is((await promiseName), expected, "got the expected sanitized name");
+  }
+
+  let promise = new Promise(function(resolve) {
+    chromeScript.addMessageListener("unregistered", function listener() {
+      chromeScript.removeMessageListener("unregistered", listener);
+      resolve();
+    });
+  });
+  chromeScript.sendAsyncMessage("unregister");
+  await promise;
+
+  chromeScript.destroy();
+});
+</script>
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/test_unknown_ext_protocol_handlers.html b/uriloader/exthandler/tests/mochitest/test_unknown_ext_protocol_handlers.html
new file mode 100644
index 0000000000..f8727db605
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/test_unknown_ext_protocol_handlers.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Test for no error reporting for unknown external protocols</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<iframe id="testFrame"></iframe>
+<script type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+window.onload = () => {
+  let testFrame = document.getElementById("testFrame");
+
+  try {
+    testFrame.contentWindow.location.href = "unknownextproto:";
+    ok(true, "There is no error reporting for unknown external protocol navigation.");
+  } catch (e) {
+    ok(false, "There should be no error reporting for unknown external protocol navigation.");
+  }
+
+  SimpleTest.finish();
+};
+</script>
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/test_unsafeBidiChars.xhtml b/uriloader/exthandler/tests/mochitest/test_unsafeBidiChars.xhtml
new file mode 100644
index 0000000000..4f62b32d99
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/test_unsafeBidiChars.xhtml
@@ -0,0 +1,72 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Test for Handling of unsafe bidi chars</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<iframe id="test"></iframe>
+<script type="text/javascript">
+var unsafeBidiChars = [
+  "\xe2\x80\xaa", // LRE
+  "\xe2\x80\xab", // RLE
+  "\xe2\x80\xac", // PDF
+  "\xe2\x80\xad", // LRO
+  "\xe2\x80\xae",  // RLO
+];
+
+var tests = [
+  "{1}.test",
+  "{1}File.test",
+  "Fi{1}le.test",
+  "File{1}.test",
+  "File.{1}test",
+  "File.te{1}st",
+  "File.test{1}",
+  "File.{1}",
+];
+
+function replace(name, x) {
+  return name.replace(/\{1\}/, x);
+}
+
+function sanitize(name) {
+  return replace(name, "_");
+}
+
+add_task(async function() {
+  let url = SimpleTest.getTestFileURL("HelperAppLauncherDialog_chromeScript.js");
+  let chromeScript = SpecialPowers.loadChromeScript(url);
+
+  for (let test of tests) {
+    for (let char of unsafeBidiChars) {
+      let promiseName = new Promise(function(resolve) {
+        chromeScript.addMessageListener("suggestedFileName",
+                                        function listener(data) {
+          chromeScript.removeMessageListener("suggestedFileName", listener);
+          resolve(data);
+        });
+      });
+      let name = replace(test, char);
+      let expected = sanitize(test);
+      document.getElementById("test").src =
+        "unsafeBidiFileName.sjs?name=" + encodeURIComponent(name);
+      is((await promiseName), expected, "got the expected sanitized name");
+    }
+  }
+
+  let promise = new Promise(function(resolve) {
+    chromeScript.addMessageListener("unregistered", function listener() {
+      chromeScript.removeMessageListener("unregistered", listener);
+      resolve();
+    });
+  });
+  chromeScript.sendAsyncMessage("unregister");
+  await promise;
+
+  chromeScript.destroy();
+});
+</script>
+</body>
+</html>
diff --git a/uriloader/exthandler/tests/mochitest/unsafeBidiFileName.sjs b/uriloader/exthandler/tests/mochitest/unsafeBidiFileName.sjs
new file mode 100644
index 0000000000..48301be5b4
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/unsafeBidiFileName.sjs
@@ -0,0 +1,14 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function handleRequest(request, response) {
+  response.setStatusLine(request.httpVersion, 200, "OK");
+
+  if (!request.queryString.match(/^name=/))
+    return;
+  var name = decodeURIComponent(request.queryString.substring(5));
+
+  response.setHeader("Content-Type", "application/octet-stream; name=\"" + name + "\"");
+  response.setHeader("Content-Disposition", "inline; filename=\"" + name + "\"");
+}
diff --git a/uriloader/exthandler/tests/moz.build b/uriloader/exthandler/tests/moz.build
new file mode 100644
index 0000000000..3d96aaa448
--- /dev/null
+++ b/uriloader/exthandler/tests/moz.build
@@ -0,0 +1,31 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+MOCHITEST_MANIFESTS += ["mochitest/mochitest.ini"]
+
+XPCSHELL_TESTS_MANIFESTS += ["unit/xpcshell.ini"]
+
+BROWSER_CHROME_MANIFESTS += ["mochitest/browser.ini"]
+
+TESTING_JS_MODULES += [
+    "HandlerServiceTestUtils.jsm",
+]
+
+GeckoSimplePrograms(
+    [
+        "WriteArgument",
+    ],
+    linkage=None,
+)
+
+if CONFIG["COMPILE_ENVIRONMENT"]:
+    TEST_HARNESS_FILES.xpcshell.uriloader.exthandler.tests.unit += [
+        "!WriteArgument%s" % CONFIG["BIN_SUFFIX"]
+    ]
+
+USE_LIBS += [
+    "nspr",
+]
diff --git a/uriloader/exthandler/tests/unit/handlers.json b/uriloader/exthandler/tests/unit/handlers.json
new file mode 100644
index 0000000000..40e88f930a
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/handlers.json
@@ -0,0 +1,90 @@
+{
+  "defaultHandlersVersion": {
+    "en-US": 999
+  },
+  "mimeTypes": {
+    "example/type.handleinternally": {
+      "unknownProperty": "preserved",
+      "action": 3,
+      "extensions": [
+        "example_one"
+      ]
+    },
+    "example/type.savetodisk": {
+      "action": 0,
+      "ask": true,
+      "handlers": [
+        {
+          "name": "Example Default Handler",
+          "uriTemplate": "https://www.example.com/?url=%s"
+        }
+      ],
+      "extensions": [
+        "example_two",
+        "example_three"
+      ]
+    },
+    "example/type.usehelperapp": {
+      "action": 2,
+      "ask": true,
+      "handlers": [
+        {
+          "name": "Example Default Handler",
+          "uriTemplate": "https://www.example.com/?url=%s"
+        },
+        {
+          "name": "Example Possible Handler One",
+          "uriTemplate": "http://www.example.com/?id=1&url=%s"
+        },
+        {
+          "name": "Example Possible Handler Two",
+          "uriTemplate": "http://www.example.com/?id=2&url=%s"
+        }
+      ],
+      "extensions": [
+        "example_two",
+        "example_three"
+      ]
+    },
+    "example/type.usesystemdefault": {
+      "action": 4,
+      "handlers": [
+        null,
+        {
+          "name": "Example Possible Handler",
+          "uriTemplate": "http://www.example.com/?url=%s"
+        }
+      ]
+    }
+  },
+  "schemes": {
+    "examplescheme.usehelperapp": {
+      "action": 2,
+      "ask": true,
+      "handlers": [
+        {
+          "name": "Example Default Handler",
+          "uriTemplate": "https://www.example.com/?url=%s"
+        },
+        {
+          "name": "Example Possible Handler One",
+          "uriTemplate": "http://www.example.com/?id=1&url=%s"
+        },
+        {
+          "name": "Example Possible Handler Two",
+          "uriTemplate": "http://www.example.com/?id=2&url=%s"
+        }
+      ]
+    },
+    "examplescheme.usesystemdefault": {
+      "action": 4,
+      "handlers": [
+        null,
+        {
+          "name": "Example Possible Handler",
+          "uriTemplate": "http://www.example.com/?url=%s"
+        }
+      ]
+    }
+  }
+}
diff --git a/uriloader/exthandler/tests/unit/head.js b/uriloader/exthandler/tests/unit/head.js
new file mode 100644
index 0000000000..3330a309be
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/head.js
@@ -0,0 +1,79 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Initialization for tests related to invoking external handler applications.
+ */
+
+"use strict";
+
+var { AppConstants } = ChromeUtils.import(
+  "resource://gre/modules/AppConstants.jsm"
+);
+var { FileUtils } = ChromeUtils.import("resource://gre/modules/FileUtils.jsm");
+var { NetUtil } = ChromeUtils.import("resource://gre/modules/NetUtil.jsm");
+var { OS, require } = ChromeUtils.import("resource://gre/modules/osfile.jsm");
+var { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+var { XPCOMUtils } = ChromeUtils.import(
+  "resource://gre/modules/XPCOMUtils.jsm"
+);
+
+ChromeUtils.import(
+  "resource://testing-common/HandlerServiceTestUtils.jsm",
+  this
+);
+var { TestUtils } = ChromeUtils.import(
+  "resource://testing-common/TestUtils.jsm"
+);
+
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gHandlerService",
+  "@mozilla.org/uriloader/handler-service;1",
+  "nsIHandlerService"
+);
+
+do_get_profile();
+
+let jsonPath = OS.Path.join(OS.Constants.Path.profileDir, "handlers.json");
+
+/**
+ * Unloads the nsIHandlerService data store, so the back-end file can be
+ * accessed or modified, and the new data will be loaded at the next access.
+ */
+let unloadHandlerStore = async function() {
+  // If this function is called before the nsIHandlerService instance has been
+  // initialized for the first time, the observer below will not be registered.
+  // We have to force initialization to prevent the function from stalling.
+  gHandlerService;
+
+  let promise = TestUtils.topicObserved("handlersvc-json-replace-complete");
+  Services.obs.notifyObservers(null, "handlersvc-json-replace");
+  await promise;
+};
+
+/**
+ * Unloads the data store and deletes it.
+ */
+let deleteHandlerStore = async function() {
+  await unloadHandlerStore();
+
+  await OS.File.remove(jsonPath, { ignoreAbsent: true });
+};
+
+/**
+ * Unloads the data store and replaces it with the test data file.
+ */
+let copyTestDataToHandlerStore = async function() {
+  await unloadHandlerStore();
+
+  await OS.File.copy(do_get_file("handlers.json").path, jsonPath);
+};
+
+/**
+ * Ensures the files are removed and the services unloaded when the tests end.
+ */
+registerCleanupFunction(async function test_terminate() {
+  await deleteHandlerStore();
+});
diff --git a/uriloader/exthandler/tests/unit/mailcap b/uriloader/exthandler/tests/unit/mailcap
new file mode 100644
index 0000000000..dc93ef8042
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/mailcap
@@ -0,0 +1,2 @@
+text/plain; cat '%s'; needsterminal
+text/plain; sed '%s'
diff --git a/uriloader/exthandler/tests/unit/test_badMIMEType.js b/uriloader/exthandler/tests/unit/test_badMIMEType.js
new file mode 100644
index 0000000000..49c5e8d848
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_badMIMEType.js
@@ -0,0 +1,29 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function run_test() {
+  // "text/plain" has an 0xFF character appended to it.  This means it's an
+  // invalid string, which is tricky to enter using a text editor (I used
+  // emacs' hexl-mode).  It also means an ordinary text editor might drop it
+  // or convert it to something that *is* valid (in UTF8).  So we measure
+  // its length to make sure this hasn't happened.
+  var badMimeType = "text/plainÿ";
+  Assert.equal(badMimeType.length, 11);
+  try {
+    Cc["@mozilla.org/mime;1"]
+      .getService(Ci.nsIMIMEService)
+      .getFromTypeAndExtension(badMimeType, "txt");
+  } catch (e) {
+    if (
+      !(e instanceof Ci.nsIException) ||
+      e.result != Cr.NS_ERROR_NOT_AVAILABLE
+    ) {
+      throw e;
+    }
+    // This is an expected exception, thrown if the type can't be determined
+  }
+  // Not crashing is good enough
+  Assert.equal(true, true);
+}
diff --git a/uriloader/exthandler/tests/unit/test_defaults_handlerService.js b/uriloader/exthandler/tests/unit/test_defaults_handlerService.js
new file mode 100644
index 0000000000..f9f9feda23
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_defaults_handlerService.js
@@ -0,0 +1,163 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gExternalProtocolService",
+  "@mozilla.org/uriloader/external-protocol-service;1",
+  "nsIExternalProtocolService"
+);
+
+const kDefaultHandlerList = Services.prefs
+  .getChildList("gecko.handlerService.schemes")
+  .filter(p => {
+    try {
+      let val = Services.prefs.getComplexValue(p, Ci.nsIPrefLocalizedString)
+        .data;
+      return !!val;
+    } catch (ex) {
+      return false;
+    }
+  });
+
+add_task(async function test_check_defaults_get_added() {
+  let protocols = new Set(
+    kDefaultHandlerList.map(p => p.match(/schemes\.(\w+)/)[1])
+  );
+  for (let protocol of protocols) {
+    const kPrefStr = `schemes.${protocol}.`;
+    let matchingPrefs = kDefaultHandlerList.filter(p => p.includes(kPrefStr));
+    let protocolHandlerCount = matchingPrefs.length / 2;
+    Assert.ok(
+      protocolHandlerCount,
+      `Prefs for ${protocol} have at least 1 protocol handler`
+    );
+    Assert.ok(
+      gHandlerService.wrappedJSObject._store.data.schemes[protocol].stubEntry,
+      `Expect stub for ${protocol}`
+    );
+    let info = gExternalProtocolService.getProtocolHandlerInfo(protocol, {});
+    Assert.ok(
+      info,
+      `Should be able to get protocol handler info for ${protocol}`
+    );
+    let handlers = Array.from(
+      info.possibleApplicationHandlers.enumerate(Ci.nsIHandlerApp)
+    );
+    handlers = handlers.filter(h => h instanceof Ci.nsIWebHandlerApp);
+    Assert.equal(
+      handlers.length,
+      protocolHandlerCount,
+      `Default web handlers for ${protocol} should match`
+    );
+    let { alwaysAskBeforeHandling, preferredAction } = info;
+    // Actually store something, pretending there was a change:
+    let infoToWrite = gExternalProtocolService.getProtocolHandlerInfo(
+      protocol,
+      {}
+    );
+    gHandlerService.store(infoToWrite);
+    ok(
+      !gHandlerService.wrappedJSObject._store.data.schemes[protocol].stubEntry,
+      "Expect stub entry info to go away"
+    );
+
+    let newInfo = gExternalProtocolService.getProtocolHandlerInfo(protocol, {});
+    Assert.equal(
+      alwaysAskBeforeHandling,
+      newInfo.alwaysAskBeforeHandling,
+      protocol + " - always ask shouldn't change"
+    );
+    Assert.equal(
+      preferredAction,
+      newInfo.preferredAction,
+      protocol + " - preferred action shouldn't change"
+    );
+    await deleteHandlerStore();
+  }
+});
+
+add_task(async function test_check_default_modification() {
+  let mailtoHandlerCount =
+    kDefaultHandlerList.filter(p => p.includes("mailto")).length / 2;
+  Assert.ok(mailtoHandlerCount, "Prefs have at least 1 mailto handler");
+  Assert.ok(
+    true,
+    JSON.stringify(gHandlerService.wrappedJSObject._store.data.schemes.mailto)
+  );
+  Assert.ok(
+    gHandlerService.wrappedJSObject._store.data.schemes.mailto.stubEntry,
+    "Expect stub for mailto"
+  );
+  let mailInfo = gExternalProtocolService.getProtocolHandlerInfo("mailto", {});
+  mailInfo.alwaysAskBeforeHandling = false;
+  mailInfo.preferredAction = Ci.nsIHandlerInfo.useSystemDefault;
+  gHandlerService.store(mailInfo);
+  Assert.ok(
+    !gHandlerService.wrappedJSObject._store.data.schemes.mailto.stubEntry,
+    "Stub entry should be removed immediately."
+  );
+  let newMail = gExternalProtocolService.getProtocolHandlerInfo("mailto", {});
+  Assert.equal(newMail.preferredAction, Ci.nsIHandlerInfo.useSystemDefault);
+  Assert.equal(newMail.alwaysAskBeforeHandling, false);
+  await deleteHandlerStore();
+});
+
+/**
+ * Check that we don't add bogus handlers.
+ */
+add_task(async function test_check_restrictions() {
+  const kTestData = {
+    testdeleteme: [
+      ["Delete me", ""],
+      ["Delete me insecure", "http://example.com/%s"],
+      ["Delete me no substitution", "https://example.com/"],
+      ["Keep me", "https://example.com/%s"],
+    ],
+    testreallydeleteme: [
+      // used to check we remove the entire entry.
+      ["Delete me", "http://example.com/%s"],
+    ],
+  };
+  for (let [scheme, handlers] of Object.entries(kTestData)) {
+    let count = 1;
+    for (let [name, uriTemplate] of handlers) {
+      let pref = `gecko.handlerService.schemes.${scheme}.${count}.`;
+      let obj = Cc["@mozilla.org/pref-localizedstring;1"].createInstance(
+        Ci.nsIPrefLocalizedString
+      );
+      obj.data = name;
+      Services.prefs.setComplexValue(
+        pref + "name",
+        Ci.nsIPrefLocalizedString,
+        obj
+      );
+      obj.data = uriTemplate;
+      Services.prefs.setComplexValue(
+        pref + "uriTemplate",
+        Ci.nsIPrefLocalizedString,
+        obj
+      );
+      count++;
+    }
+  }
+
+  gHandlerService.wrappedJSObject._injectDefaultProtocolHandlers();
+  let schemeData = gHandlerService.wrappedJSObject._store.data.schemes;
+
+  Assert.ok(schemeData.testdeleteme, "Expect an entry for testdeleteme");
+  Assert.ok(
+    schemeData.testdeleteme.stubEntry,
+    "Expect a stub entry for testdeleteme"
+  );
+
+  Assert.deepEqual(
+    schemeData.testdeleteme.handlers,
+    [null, { name: "Keep me", uriTemplate: "https://example.com/%s" }],
+    "Expect only one handler is kept."
+  );
+
+  Assert.ok(!schemeData.testreallydeleteme, "No entry for reallydeleteme");
+});
diff --git a/uriloader/exthandler/tests/unit/test_getMIMEInfo_pdf.js b/uriloader/exthandler/tests/unit/test_getMIMEInfo_pdf.js
new file mode 100644
index 0000000000..62031da1e6
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_getMIMEInfo_pdf.js
@@ -0,0 +1,36 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gMIMEService",
+  "@mozilla.org/mime;1",
+  "nsIMIMEService"
+);
+XPCOMUtils.defineLazyServiceGetter(
+  this,
+  "gBundleService",
+  "@mozilla.org/intl/stringbundle;1",
+  "nsIStringBundleService"
+);
+
+// PDF files should always have a generic description instead
+// of relying on what is registered with the Operating System.
+add_task(async function test_check_unknown_mime_type() {
+  const mimeService = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  let pdfType = mimeService.getTypeFromExtension("pdf");
+  Assert.equal(pdfType, "application/pdf");
+  let extension = mimeService.getPrimaryExtension("application/pdf", "");
+  Assert.equal(extension, "pdf", "Expect pdf extension when given mime");
+  let mimeInfo = gMIMEService.getFromTypeAndExtension("", "pdf");
+  let stringBundle = gBundleService.createBundle(
+    "chrome://mozapps/locale/downloads/unknownContentType.properties"
+  );
+  Assert.equal(
+    mimeInfo.description,
+    stringBundle.GetStringFromName("pdfExtHandlerDescription"),
+    "PDF has generic description"
+  );
+});
diff --git a/uriloader/exthandler/tests/unit/test_getMIMEInfo_unknown_mime_type.js b/uriloader/exthandler/tests/unit/test_getMIMEInfo_unknown_mime_type.js
new file mode 100644
index 0000000000..9beef9d9c5
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_getMIMEInfo_unknown_mime_type.js
@@ -0,0 +1,32 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Zip files can be opened by Windows explorer, so we should always be able to
+// determine a description and default handler for them. However, things can
+// get messy if they are sent to us with a mime type other than what Windows
+// considers the "right" mimetype (application/x-zip-compressed), like
+// application/zip, which is what most places (IANA, macOS, probably all linux
+// distros, Apache, etc.) think is the "right" mimetype.
+add_task(async function test_check_unknown_mime_type() {
+  const mimeService = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+  let zipType = mimeService.getTypeFromExtension("zip");
+  Assert.equal(zipType, "application/x-zip-compressed");
+  try {
+    let extension = mimeService.getPrimaryExtension("application/zip", "");
+    Assert.equal(
+      extension,
+      "zip",
+      "Expect our own info to provide an extension for zip files."
+    );
+  } catch (ex) {
+    Assert.ok(false, "We shouldn't throw when getting zip info.");
+  }
+  let found = {};
+  let mimeInfo = mimeService.getMIMEInfoFromOS("application/zip", "zip", found);
+  Assert.ok(
+    mimeInfo.hasDefaultHandler,
+    "Should have a default app for zip files"
+  );
+});
diff --git a/uriloader/exthandler/tests/unit/test_getTypeFromExtension_ext_to_type_mapping.js b/uriloader/exthandler/tests/unit/test_getTypeFromExtension_ext_to_type_mapping.js
new file mode 100644
index 0000000000..7202db58de
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_getTypeFromExtension_ext_to_type_mapping.js
@@ -0,0 +1,65 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Test for bug 508030 <https://bugzilla.mozilla.org/show_bug.cgi?id=508030>:
+ * nsIMIMEService.getTypeFromExtension fails to find a match in the
+ * "ext-to-type-mapping" category if the provided extension is not lowercase.
+ */
+function run_test() {
+  // --- Common services ---
+
+  const mimeService = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+
+  const categoryManager = Services.catMan;
+
+  // --- Test procedure ---
+
+  const kTestExtension = "testextension";
+  const kTestExtensionMixedCase = "testExtensIon";
+  const kTestMimeType = "application/x-testextension";
+
+  // Ensure that the test extension is not initially recognized by the operating
+  // system or the "ext-to-type-mapping" category.
+  try {
+    // Try and get the MIME type associated with the extension.
+    mimeService.getTypeFromExtension(kTestExtension);
+    // The line above should have thrown an exception.
+    do_throw("nsIMIMEService.getTypeFromExtension succeeded unexpectedly");
+  } catch (e) {
+    if (
+      !(e instanceof Ci.nsIException) ||
+      e.result != Cr.NS_ERROR_NOT_AVAILABLE
+    ) {
+      throw e;
+    }
+    // This is an expected exception, thrown if the type can't be determined.
+    // Any other exception would cause the test to fail.
+  }
+
+  // Add a temporary category entry mapping the extension to the MIME type.
+  categoryManager.addCategoryEntry(
+    "ext-to-type-mapping",
+    kTestExtension,
+    kTestMimeType,
+    false,
+    true
+  );
+
+  // Check that the mapping is recognized in the simple case.
+  var type = mimeService.getTypeFromExtension(kTestExtension);
+  Assert.equal(type, kTestMimeType);
+
+  // Check that the mapping is recognized even if the extension has mixed case.
+  type = mimeService.getTypeFromExtension(kTestExtensionMixedCase);
+  Assert.equal(type, kTestMimeType);
+
+  // Clean up after ourselves.
+  categoryManager.deleteCategoryEntry(
+    "ext-to-type-mapping",
+    kTestExtension,
+    false
+  );
+}
diff --git a/uriloader/exthandler/tests/unit/test_getTypeFromExtension_with_empty_Content_Type.js b/uriloader/exthandler/tests/unit/test_getTypeFromExtension_with_empty_Content_Type.js
new file mode 100644
index 0000000000..dad5530856
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_getTypeFromExtension_with_empty_Content_Type.js
@@ -0,0 +1,190 @@
+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Test for bug 484579 <https://bugzilla.mozilla.org/show_bug.cgi?id=484579>:
+ * nsIMIMEService.getTypeFromExtension may fail unexpectedly on Windows when
+ * "Content Type" is empty in the registry.
+ */
+
+// We must use a file extension that isn't listed in nsExternalHelperAppService's
+// defaultMimeEntries, otherwise the code takes a shortcut skipping the registry.
+const FILE_EXTENSION = ".nfo";
+// This is used to ensure the test properly used the mock, so that if we change
+// the underlying code, it won't be skipped.
+let gTestUsedOurMock = false;
+
+function run_test() {
+  // Activate the override of the file association data in the registry.
+  registerMockWindowsRegKeyFactory();
+
+  // Check the mock has been properly activated.
+  let regKey = Cc["@mozilla.org/windows-registry-key;1"].createInstance(
+    Ci.nsIWindowsRegKey
+  );
+  regKey.open(
+    Ci.nsIWindowsRegKey.ROOT_KEY_CLASSES_ROOT,
+    FILE_EXTENSION,
+    Ci.nsIWindowsRegKey.ACCESS_QUERY_VALUE
+  );
+  Assert.equal(
+    regKey.readStringValue("content type"),
+    "",
+    "Check the mock replied as expected."
+  );
+  Assert.ok(gTestUsedOurMock, "The test properly used the mock registry");
+  // Reset gTestUsedOurMock, because we just used it.
+  gTestUsedOurMock = false;
+  // Try and get the MIME type associated with the extension. If this
+  // operation does not throw an unexpected exception, the test succeeds.
+  Assert.throws(
+    () => {
+      Cc["@mozilla.org/mime;1"]
+        .getService(Ci.nsIMIMEService)
+        .getTypeFromExtension(FILE_EXTENSION);
+    },
+    /NS_ERROR_NOT_AVAILABLE/,
+    "Should throw a NOT_AVAILABLE exception"
+  );
+
+  Assert.ok(gTestUsedOurMock, "The test properly used the mock registry");
+}
+
+/**
+ * Constructs a new mock registry key by wrapping the provided object.
+ *
+ * This mock implementation is tailored for this test, and forces consumers
+ * of the readStringValue method to believe that the "Content Type" value of
+ * the FILE_EXTENSION key under HKEY_CLASSES_ROOT is an empty string.
+ *
+ * The same value read from "HKEY_LOCAL_MACHINE\SOFTWARE\Classes" is not
+ * affected.
+ *
+ * @param aWrappedObject   An actual nsIWindowsRegKey implementation.
+ */
+function MockWindowsRegKey(aWrappedObject) {
+  this._wrappedObject = aWrappedObject;
+
+  // This function creates a forwarding function for wrappedObject
+  function makeForwardingFunction(functionName) {
+    return function() {
+      return aWrappedObject[functionName].apply(aWrappedObject, arguments);
+    };
+  }
+
+  // Forward all the functions that are not explicitly overridden
+  for (var propertyName in aWrappedObject) {
+    if (!(propertyName in this)) {
+      if (typeof aWrappedObject[propertyName] == "function") {
+        this[propertyName] = makeForwardingFunction(propertyName);
+      } else {
+        this[propertyName] = aWrappedObject[propertyName];
+      }
+    }
+  }
+}
+
+MockWindowsRegKey.prototype = {
+  // --- Overridden nsISupports interface functions ---
+
+  QueryInterface: ChromeUtils.generateQI(["nsIWindowsRegKey"]),
+
+  // --- Overridden nsIWindowsRegKey interface functions ---
+
+  open(aRootKey, aRelPath, aMode) {
+    // Remember the provided root key and path
+    this._rootKey = aRootKey;
+    this._relPath = aRelPath;
+
+    // Create the actual registry key
+    return this._wrappedObject.open(aRootKey, aRelPath, aMode);
+  },
+
+  openChild(aRelPath, aMode) {
+    // Open the child key and wrap it
+    var innerKey = this._wrappedObject.openChild(aRelPath, aMode);
+    var key = new MockWindowsRegKey(innerKey);
+
+    // Set the properties of the child key and return it
+    key._rootKey = this._rootKey;
+    key._relPath = this._relPath + aRelPath;
+    return key;
+  },
+
+  createChild(aRelPath, aMode) {
+    // Create the child key and wrap it
+    var innerKey = this._wrappedObject.createChild(aRelPath, aMode);
+    var key = new MockWindowsRegKey(innerKey);
+
+    // Set the properties of the child key and return it
+    key._rootKey = this._rootKey;
+    key._relPath = this._relPath + aRelPath;
+    return key;
+  },
+
+  get childCount() {
+    return this._wrappedObject.childCount;
+  },
+
+  get valueCount() {
+    return this._wrappedObject.valueCount;
+  },
+
+  readStringValue(aName) {
+    // If this is the key under test, return a fake value
+    if (
+      this._rootKey == Ci.nsIWindowsRegKey.ROOT_KEY_CLASSES_ROOT &&
+      this._relPath.toLowerCase() == FILE_EXTENSION &&
+      aName.toLowerCase() == "content type"
+    ) {
+      gTestUsedOurMock = true;
+      return "";
+    }
+    // Return the real value from the registry
+    return this._wrappedObject.readStringValue(aName);
+  },
+};
+
+function registerMockWindowsRegKeyFactory() {
+  const kMockCID = Components.ID("{9b23dfe9-296b-4740-ba1c-d39c9a16e55e}");
+  const kWindowsRegKeyContractID = "@mozilla.org/windows-registry-key;1";
+  // Preserve the original CID.
+  let originalWindowsRegKeyCID = Cc[kWindowsRegKeyContractID].number;
+
+  info("Create a mock RegKey factory");
+  let originalRegKey = Cc["@mozilla.org/windows-registry-key;1"].createInstance(
+    Ci.nsIWindowsRegKey
+  );
+  let mockWindowsRegKeyFactory = {
+    createInstance(outer, iid) {
+      if (outer != null) {
+        throw Components.Exception("", Cr.NS_ERROR_NO_AGGREGATION);
+      }
+      info("Create a mock wrapper around RegKey");
+      var key = new MockWindowsRegKey(originalRegKey);
+      return key.QueryInterface(iid);
+    },
+  };
+  info("Register the mock RegKey factory");
+  let registrar = Components.manager.QueryInterface(Ci.nsIComponentRegistrar);
+  registrar.registerFactory(
+    kMockCID,
+    "Mock Windows Registry Key Implementation",
+    kWindowsRegKeyContractID,
+    mockWindowsRegKeyFactory
+  );
+
+  registerCleanupFunction(() => {
+    // Free references to the mock factory
+    registrar.unregisterFactory(kMockCID, mockWindowsRegKeyFactory);
+    // Restore the original factory
+    registrar.registerFactory(
+      Components.ID(originalWindowsRegKeyCID),
+      "",
+      kWindowsRegKeyContractID,
+      null
+    );
+  });
+}
diff --git a/uriloader/exthandler/tests/unit/test_handlerService.js b/uriloader/exthandler/tests/unit/test_handlerService.js
new file mode 100644
index 0000000000..610eb5b749
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_handlerService.js
@@ -0,0 +1,474 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function run_test() {
+  //* *************************************************************************//
+  // Constants
+
+  const handlerSvc = Cc["@mozilla.org/uriloader/handler-service;1"].getService(
+    Ci.nsIHandlerService
+  );
+
+  const mimeSvc = Cc["@mozilla.org/mime;1"].getService(Ci.nsIMIMEService);
+
+  const protoSvc = Cc[
+    "@mozilla.org/uriloader/external-protocol-service;1"
+  ].getService(Ci.nsIExternalProtocolService);
+
+  const prefSvc = Services.prefs;
+
+  const env = Cc["@mozilla.org/process/environment;1"].getService(
+    Ci.nsIEnvironment
+  );
+
+  const rootPrefBranch = prefSvc.getBranch("");
+
+  let noMailto = false;
+  if (mozinfo.os == "win") {
+    // Check mailto handler from registry.
+    // If registry entry is nothing, no mailto handler
+    let regSvc = Cc["@mozilla.org/windows-registry-key;1"].createInstance(
+      Ci.nsIWindowsRegKey
+    );
+    try {
+      regSvc.open(regSvc.ROOT_KEY_CLASSES_ROOT, "mailto", regSvc.ACCESS_READ);
+      noMailto = false;
+    } catch (ex) {
+      noMailto = true;
+    }
+    regSvc.close();
+  }
+
+  if (mozinfo.os == "linux") {
+    // Check mailto handler from GIO
+    // If there isn't one, then we have no mailto handler
+    let gIOSvc = Cc["@mozilla.org/gio-service;1"].createInstance(
+      Ci.nsIGIOService
+    );
+    try {
+      gIOSvc.getAppForURIScheme("mailto");
+      noMailto = false;
+    } catch (ex) {
+      noMailto = true;
+    }
+  }
+
+  //* *************************************************************************//
+  // Sample Data
+
+  // It doesn't matter whether or not this nsIFile is actually executable,
+  // only that it has a path and exists.  Since we don't know any executable
+  // that exists on all platforms (except possibly the application being
+  // tested, but there doesn't seem to be a way to get a reference to that
+  // from the directory service), we use the temporary directory itself.
+  var executable = Services.dirsvc.get("TmpD", Ci.nsIFile);
+  // XXX We could, of course, create an actual executable in the directory:
+  // executable.append("localhandler");
+  // if (!executable.exists())
+  //  executable.create(Ci.nsIFile.NORMAL_FILE_TYPE, 0o755);
+
+  var localHandler = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  localHandler.name = "Local Handler";
+  localHandler.executable = executable;
+
+  var webHandler = Cc[
+    "@mozilla.org/uriloader/web-handler-app;1"
+  ].createInstance(Ci.nsIWebHandlerApp);
+  webHandler.name = "Web Handler";
+  webHandler.uriTemplate = "http://www.example.com/?%s";
+
+  // FIXME: these tests create and manipulate enough variables that it would
+  // make sense to move each test into its own scope so we don't run the risk
+  // of one test stomping on another's data.
+
+  //* *************************************************************************//
+  // Test Default Properties
+
+  // Get a handler info for a MIME type that neither the application nor
+  // the OS knows about and make sure its properties are set to the proper
+  // default values.
+
+  var handlerInfo = mimeSvc.getFromTypeAndExtension("nonexistent/type", null);
+
+  // Make sure it's also an nsIHandlerInfo.
+  Assert.ok(handlerInfo instanceof Ci.nsIHandlerInfo);
+
+  Assert.equal(handlerInfo.type, "nonexistent/type");
+
+  // Deprecated property, but we should still make sure it's set correctly.
+  Assert.equal(handlerInfo.MIMEType, "nonexistent/type");
+
+  // These properties are the ones the handler service knows how to store.
+  Assert.equal(handlerInfo.preferredAction, Ci.nsIHandlerInfo.saveToDisk);
+  Assert.equal(handlerInfo.preferredApplicationHandler, null);
+  Assert.equal(handlerInfo.possibleApplicationHandlers.length, 0);
+  Assert.ok(handlerInfo.alwaysAskBeforeHandling);
+
+  // These properties are initialized to default values by the service,
+  // so we might as well make sure they're initialized to the right defaults.
+  Assert.equal(handlerInfo.description, "");
+  Assert.equal(handlerInfo.hasDefaultHandler, false);
+  Assert.equal(handlerInfo.defaultDescription, "");
+
+  // test some default protocol info properties
+  var haveDefaultHandlersVersion = false;
+  try {
+    // If we have a defaultHandlersVersion pref, then assume that we're in the
+    // firefox tree and that we'll also have default handlers.
+    // Bug 395131 has been filed to make this test work more generically
+    // by providing our own prefs for this test rather than this icky
+    // special casing.
+    rootPrefBranch.getCharPref("gecko.handlerService.defaultHandlersVersion");
+    haveDefaultHandlersVersion = true;
+  } catch (ex) {}
+
+  const kExternalWarningDefault =
+    "network.protocol-handler.warn-external-default";
+  prefSvc.setBoolPref(kExternalWarningDefault, true);
+
+  // XXX add more thorough protocol info property checking
+
+  // no OS default handler exists
+  var protoInfo = protoSvc.getProtocolHandlerInfo("x-moz-rheet");
+  Assert.equal(protoInfo.preferredAction, protoInfo.alwaysAsk);
+  Assert.ok(protoInfo.alwaysAskBeforeHandling);
+
+  // OS default exists, injected default does not exist,
+  // explicit warning pref: false
+  const kExternalWarningPrefPrefix = "network.protocol-handler.warn-external.";
+  prefSvc.setBoolPref(kExternalWarningPrefPrefix + "http", false);
+  protoInfo = protoSvc.getProtocolHandlerInfo("http");
+  Assert.equal(0, protoInfo.possibleApplicationHandlers.length);
+  Assert.ok(!protoInfo.alwaysAskBeforeHandling);
+
+  // OS default exists, injected default does not exist,
+  // explicit warning pref: true
+  prefSvc.setBoolPref(kExternalWarningPrefPrefix + "http", true);
+  protoInfo = protoSvc.getProtocolHandlerInfo("http");
+  // OS handler isn't included in possibleApplicationHandlers, so length is 0
+  // Once they become instances of nsILocalHandlerApp, this number will need
+  // to change.
+  Assert.equal(0, protoInfo.possibleApplicationHandlers.length);
+  Assert.ok(protoInfo.alwaysAskBeforeHandling);
+
+  // OS default exists, injected default exists, explicit warning pref: false
+  prefSvc.setBoolPref(kExternalWarningPrefPrefix + "mailto", false);
+  protoInfo = protoSvc.getProtocolHandlerInfo("mailto");
+  if (haveDefaultHandlersVersion) {
+    Assert.equal(2, protoInfo.possibleApplicationHandlers.length);
+  } else {
+    Assert.equal(0, protoInfo.possibleApplicationHandlers.length);
+  }
+
+  // Win7+ or Linux's GIO might not have a default mailto: handler
+  if (noMailto) {
+    Assert.ok(protoInfo.alwaysAskBeforeHandling);
+  } else {
+    Assert.ok(!protoInfo.alwaysAskBeforeHandling);
+  }
+
+  // OS default exists, injected default exists, explicit warning pref: true
+  prefSvc.setBoolPref(kExternalWarningPrefPrefix + "mailto", true);
+  protoInfo = protoSvc.getProtocolHandlerInfo("mailto");
+  if (haveDefaultHandlersVersion) {
+    Assert.equal(2, protoInfo.possibleApplicationHandlers.length);
+    // Win7+ or Linux's GIO may have no default mailto: handler, so we'd ask
+    // anyway. Otherwise, the default handlers will not have stored preferred
+    // actions etc., so re-requesting them after the warning pref has changed
+    // will use the updated pref value. So both when we have and do not have
+    // a default mailto: handler, we'll ask:
+    Assert.ok(protoInfo.alwaysAskBeforeHandling);
+    // As soon as anyone actually stores updated defaults into the profile
+    // database, that default will stop tracking the warning pref.
+  } else {
+    Assert.equal(0, protoInfo.possibleApplicationHandlers.length);
+    Assert.ok(protoInfo.alwaysAskBeforeHandling);
+  }
+
+  if (haveDefaultHandlersVersion) {
+    // Now set the value stored in RDF to true, and the pref to false, to make
+    // sure we still get the right value. (Basically, same thing as above but
+    // with the values reversed.)
+    prefSvc.setBoolPref(kExternalWarningPrefPrefix + "mailto", false);
+    protoInfo.alwaysAskBeforeHandling = true;
+    handlerSvc.store(protoInfo);
+    protoInfo = protoSvc.getProtocolHandlerInfo("mailto");
+    Assert.equal(2, protoInfo.possibleApplicationHandlers.length);
+    Assert.ok(protoInfo.alwaysAskBeforeHandling);
+  }
+
+  //* *************************************************************************//
+  // Test Round-Trip Data Integrity
+
+  // Test round-trip data integrity by setting the properties of the handler
+  // info object to different values, telling the handler service to store the
+  // object, and then retrieving a new info object for the same type and making
+  // sure its properties are identical.
+
+  handlerInfo.preferredAction = Ci.nsIHandlerInfo.useHelperApp;
+  handlerInfo.preferredApplicationHandler = localHandler;
+  handlerInfo.alwaysAskBeforeHandling = false;
+
+  handlerSvc.store(handlerInfo);
+
+  handlerInfo = mimeSvc.getFromTypeAndExtension("nonexistent/type", null);
+
+  Assert.equal(handlerInfo.preferredAction, Ci.nsIHandlerInfo.useHelperApp);
+
+  Assert.notEqual(handlerInfo.preferredApplicationHandler, null);
+  var preferredHandler = handlerInfo.preferredApplicationHandler;
+  Assert.equal(typeof preferredHandler, "object");
+  Assert.equal(preferredHandler.name, "Local Handler");
+  Assert.ok(preferredHandler instanceof Ci.nsILocalHandlerApp);
+  preferredHandler.QueryInterface(Ci.nsILocalHandlerApp);
+  Assert.equal(preferredHandler.executable.path, localHandler.executable.path);
+
+  Assert.ok(!handlerInfo.alwaysAskBeforeHandling);
+
+  // Make sure the handler service's enumerate method lists all known handlers.
+  var handlerInfo2 = mimeSvc.getFromTypeAndExtension("nonexistent/type2", null);
+  handlerSvc.store(handlerInfo2);
+  var handlerTypes = ["nonexistent/type", "nonexistent/type2"];
+  if (haveDefaultHandlersVersion) {
+    handlerTypes.push("mailto");
+    handlerTypes.push("irc");
+    handlerTypes.push("ircs");
+  }
+  for (let handler of handlerSvc.enumerate()) {
+    Assert.notEqual(handlerTypes.indexOf(handler.type), -1);
+    handlerTypes.splice(handlerTypes.indexOf(handler.type), 1);
+  }
+  Assert.equal(handlerTypes.length, 0);
+  // Make sure the handler service's remove method removes a handler record.
+  handlerSvc.remove(handlerInfo2);
+  let handlers = handlerSvc.enumerate();
+  while (handlers.hasMoreElements()) {
+    Assert.notEqual(
+      handlers.getNext().QueryInterface(Ci.nsIHandlerInfo).type,
+      handlerInfo2.type
+    );
+  }
+
+  // Make sure we can store and retrieve a handler info object with no preferred
+  // handler.
+  var noPreferredHandlerInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/no-preferred-handler",
+    null
+  );
+  handlerSvc.store(noPreferredHandlerInfo);
+  noPreferredHandlerInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/no-preferred-handler",
+    null
+  );
+  Assert.equal(noPreferredHandlerInfo.preferredApplicationHandler, null);
+
+  // Make sure that the handler service removes an existing handler record
+  // if we store a handler info object with no preferred handler.
+  var removePreferredHandlerInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/rem-preferred-handler",
+    null
+  );
+  removePreferredHandlerInfo.preferredApplicationHandler = localHandler;
+  handlerSvc.store(removePreferredHandlerInfo);
+  removePreferredHandlerInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/rem-preferred-handler",
+    null
+  );
+  removePreferredHandlerInfo.preferredApplicationHandler = null;
+  handlerSvc.store(removePreferredHandlerInfo);
+  removePreferredHandlerInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/rem-preferred-handler",
+    null
+  );
+  Assert.equal(removePreferredHandlerInfo.preferredApplicationHandler, null);
+
+  // Make sure we can store and retrieve a handler info object with possible
+  // handlers.  We test both adding and removing handlers.
+
+  // Get a handler info and make sure it has no possible handlers.
+  var possibleHandlersInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/possible-handlers",
+    null
+  );
+  Assert.equal(possibleHandlersInfo.possibleApplicationHandlers.length, 0);
+
+  // Store and re-retrieve the handler and make sure it still has no possible
+  // handlers.
+  handlerSvc.store(possibleHandlersInfo);
+  possibleHandlersInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/possible-handlers",
+    null
+  );
+  Assert.equal(possibleHandlersInfo.possibleApplicationHandlers.length, 0);
+
+  // Add two handlers, store the object, re-retrieve it, and make sure it has
+  // two handlers.
+  possibleHandlersInfo.possibleApplicationHandlers.appendElement(localHandler);
+  possibleHandlersInfo.possibleApplicationHandlers.appendElement(webHandler);
+  handlerSvc.store(possibleHandlersInfo);
+  possibleHandlersInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/possible-handlers",
+    null
+  );
+  Assert.equal(possibleHandlersInfo.possibleApplicationHandlers.length, 2);
+
+  // Figure out which is the local and which is the web handler and the index
+  // in the array of the local handler, which is the one we're going to remove
+  // to test removal of a handler.
+  var handler1 = possibleHandlersInfo.possibleApplicationHandlers.queryElementAt(
+    0,
+    Ci.nsIHandlerApp
+  );
+  var handler2 = possibleHandlersInfo.possibleApplicationHandlers.queryElementAt(
+    1,
+    Ci.nsIHandlerApp
+  );
+  var localPossibleHandler, webPossibleHandler, localIndex;
+  if (handler1 instanceof Ci.nsILocalHandlerApp) {
+    [localPossibleHandler, webPossibleHandler, localIndex] = [
+      handler1,
+      handler2,
+      0,
+    ];
+  } else {
+    [localPossibleHandler, webPossibleHandler, localIndex] = [
+      handler2,
+      handler1,
+      1,
+    ];
+  }
+  localPossibleHandler.QueryInterface(Ci.nsILocalHandlerApp);
+  webPossibleHandler.QueryInterface(Ci.nsIWebHandlerApp);
+
+  // Make sure the two handlers are the ones we stored.
+  Assert.equal(localPossibleHandler.name, localHandler.name);
+  Assert.ok(localPossibleHandler.equals(localHandler));
+  Assert.equal(webPossibleHandler.name, webHandler.name);
+  Assert.ok(webPossibleHandler.equals(webHandler));
+
+  // Remove a handler, store the object, re-retrieve it, and make sure
+  // it only has one handler.
+  possibleHandlersInfo.possibleApplicationHandlers.removeElementAt(localIndex);
+  handlerSvc.store(possibleHandlersInfo);
+  possibleHandlersInfo = mimeSvc.getFromTypeAndExtension(
+    "nonexistent/possible-handlers",
+    null
+  );
+  Assert.equal(possibleHandlersInfo.possibleApplicationHandlers.length, 1);
+
+  // Make sure the handler is the one we didn't remove.
+  webPossibleHandler = possibleHandlersInfo.possibleApplicationHandlers.queryElementAt(
+    0,
+    Ci.nsIWebHandlerApp
+  );
+  Assert.equal(webPossibleHandler.name, webHandler.name);
+  Assert.ok(webPossibleHandler.equals(webHandler));
+
+  // ////////////////////////////////////////////////////
+  // handler info command line parameters and equality
+  var localApp = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  var handlerApp = localApp.QueryInterface(Ci.nsIHandlerApp);
+
+  Assert.ok(handlerApp.equals(localApp));
+
+  localApp.executable = executable;
+
+  Assert.equal(0, localApp.parameterCount);
+  localApp.appendParameter("-test1");
+  Assert.equal(1, localApp.parameterCount);
+  localApp.appendParameter("-test2");
+  Assert.equal(2, localApp.parameterCount);
+  Assert.ok(localApp.parameterExists("-test1"));
+  Assert.ok(localApp.parameterExists("-test2"));
+  Assert.ok(!localApp.parameterExists("-false"));
+  localApp.clearParameters();
+  Assert.equal(0, localApp.parameterCount);
+
+  var localApp2 = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+
+  localApp2.executable = executable;
+
+  localApp.clearParameters();
+  Assert.ok(localApp.equals(localApp2));
+
+  // equal:
+  // cut -d 1 -f 2
+  // cut -d 1 -f 2
+
+  localApp.appendParameter("-test1");
+  localApp.appendParameter("-test2");
+  localApp.appendParameter("-test3");
+  localApp2.appendParameter("-test1");
+  localApp2.appendParameter("-test2");
+  localApp2.appendParameter("-test3");
+  Assert.ok(localApp.equals(localApp2));
+
+  // not equal:
+  // cut -d 1 -f 2
+  // cut -f 1 -d 2
+
+  localApp.clearParameters();
+  localApp2.clearParameters();
+
+  localApp.appendParameter("-test1");
+  localApp.appendParameter("-test2");
+  localApp.appendParameter("-test3");
+  localApp2.appendParameter("-test2");
+  localApp2.appendParameter("-test1");
+  localApp2.appendParameter("-test3");
+  Assert.ok(!localApp2.equals(localApp));
+
+  var str;
+  str = localApp.getParameter(0);
+  Assert.equal(str, "-test1");
+  str = localApp.getParameter(1);
+  Assert.equal(str, "-test2");
+  str = localApp.getParameter(2);
+  Assert.equal(str, "-test3");
+
+  // FIXME: test round trip integrity for a protocol.
+  // FIXME: test round trip integrity for a handler info with a web handler.
+
+  //* *************************************************************************//
+  // getTypeFromExtension tests
+
+  // test nonexistent extension
+  var lolType = handlerSvc.getTypeFromExtension("lolcat");
+  Assert.equal(lolType, "");
+
+  // add a handler for the extension
+  var lolHandler = mimeSvc.getFromTypeAndExtension("application/lolcat", null);
+
+  Assert.ok(!lolHandler.extensionExists("lolcat"));
+  lolHandler.preferredAction = Ci.nsIHandlerInfo.useHelperApp;
+  lolHandler.preferredApplicationHandler = localHandler;
+  lolHandler.alwaysAskBeforeHandling = false;
+  lolHandler.appendExtension("lolcat");
+
+  // store the handler
+  Assert.ok(!handlerSvc.exists(lolHandler));
+  handlerSvc.store(lolHandler);
+  Assert.ok(handlerSvc.exists(lolHandler));
+
+  // test now-existent extension
+  lolType = handlerSvc.getTypeFromExtension("lolcat");
+  Assert.equal(lolType, "application/lolcat");
+
+  // test mailcap entries with needsterminal are ignored on non-Windows non-Mac.
+  if (mozinfo.os != "win" && mozinfo.os != "mac") {
+    env.set("PERSONAL_MAILCAP", do_get_file("mailcap").path);
+    handlerInfo = mimeSvc.getFromTypeAndExtension("text/plain", null);
+    Assert.equal(
+      handlerInfo.preferredAction,
+      Ci.nsIHandlerInfo.useSystemDefault
+    );
+    Assert.equal(handlerInfo.defaultDescription, "sed");
+  }
+}
diff --git a/uriloader/exthandler/tests/unit/test_handlerService_store.js b/uriloader/exthandler/tests/unit/test_handlerService_store.js
new file mode 100644
index 0000000000..aa2efde822
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_handlerService_store.js
@@ -0,0 +1,771 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/*
+ * Tests the nsIHandlerService interface.
+ */
+
+// Set up an nsIWebHandlerApp instance that can be used in multiple tests.
+let webHandlerApp = Cc[
+  "@mozilla.org/uriloader/web-handler-app;1"
+].createInstance(Ci.nsIWebHandlerApp);
+webHandlerApp.name = "Web Handler";
+webHandlerApp.uriTemplate = "https://www.example.com/?url=%s";
+let expectedWebHandlerApp = {
+  name: webHandlerApp.name,
+  uriTemplate: webHandlerApp.uriTemplate,
+};
+
+// Set up an nsILocalHandlerApp instance that can be used in multiple tests. The
+// executable should exist, but it doesn't need to point to an actual file, so
+// we simply initialize it to the path of an existing directory.
+let localHandlerApp = Cc[
+  "@mozilla.org/uriloader/local-handler-app;1"
+].createInstance(Ci.nsILocalHandlerApp);
+localHandlerApp.name = "Local Handler";
+localHandlerApp.executable = FileUtils.getFile("TmpD", []);
+let expectedLocalHandlerApp = {
+  name: localHandlerApp.name,
+  executable: localHandlerApp.executable,
+};
+
+/**
+ * Returns a new nsIHandlerInfo instance initialized to known values that don't
+ * depend on the platform and are easier to verify later.
+ *
+ * @param type
+ *        Because the "preferredAction" is initialized to saveToDisk, this
+ *        should represent a MIME type rather than a protocol.
+ */
+function getKnownHandlerInfo(type) {
+  let handlerInfo = HandlerServiceTestUtils.getBlankHandlerInfo(type);
+  handlerInfo.preferredAction = Ci.nsIHandlerInfo.saveToDisk;
+  handlerInfo.alwaysAskBeforeHandling = false;
+  return handlerInfo;
+}
+
+/**
+ * Checks that the information stored in the handler service instance under
+ * testing matches the test data files.
+ */
+function assertAllHandlerInfosMatchTestData() {
+  let handlerInfos = HandlerServiceTestUtils.getAllHandlerInfos();
+
+  // It's important that the MIME types we check here do not exist at the
+  // operating system level, otherwise the list of handlers and file extensions
+  // will be merged. The current implementation avoids duplicate entries.
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "example/type.handleinternally",
+    preferredAction: Ci.nsIHandlerInfo.handleInternally,
+    alwaysAskBeforeHandling: false,
+    fileExtensions: ["example_one"],
+  });
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "example/type.savetodisk",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: true,
+    preferredApplicationHandler: {
+      name: "Example Default Handler",
+      uriTemplate: "https://www.example.com/?url=%s",
+    },
+    possibleApplicationHandlers: [
+      {
+        name: "Example Default Handler",
+        uriTemplate: "https://www.example.com/?url=%s",
+      },
+    ],
+    fileExtensions: ["example_two", "example_three"],
+  });
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "example/type.usehelperapp",
+    preferredAction: Ci.nsIHandlerInfo.useHelperApp,
+    alwaysAskBeforeHandling: true,
+    preferredApplicationHandler: {
+      name: "Example Default Handler",
+      uriTemplate: "https://www.example.com/?url=%s",
+    },
+    possibleApplicationHandlers: [
+      {
+        name: "Example Default Handler",
+        uriTemplate: "https://www.example.com/?url=%s",
+      },
+      {
+        name: "Example Possible Handler One",
+        uriTemplate: "http://www.example.com/?id=1&url=%s",
+      },
+      {
+        name: "Example Possible Handler Two",
+        uriTemplate: "http://www.example.com/?id=2&url=%s",
+      },
+    ],
+    fileExtensions: ["example_two", "example_three"],
+  });
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "example/type.usesystemdefault",
+    preferredAction: Ci.nsIHandlerInfo.useSystemDefault,
+    alwaysAskBeforeHandling: false,
+    possibleApplicationHandlers: [
+      {
+        name: "Example Possible Handler",
+        uriTemplate: "http://www.example.com/?url=%s",
+      },
+    ],
+  });
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "examplescheme.usehelperapp",
+    preferredAction: Ci.nsIHandlerInfo.useHelperApp,
+    alwaysAskBeforeHandling: true,
+    preferredApplicationHandler: {
+      name: "Example Default Handler",
+      uriTemplate: "https://www.example.com/?url=%s",
+    },
+    possibleApplicationHandlers: [
+      {
+        name: "Example Default Handler",
+        uriTemplate: "https://www.example.com/?url=%s",
+      },
+      {
+        name: "Example Possible Handler One",
+        uriTemplate: "http://www.example.com/?id=1&url=%s",
+      },
+      {
+        name: "Example Possible Handler Two",
+        uriTemplate: "http://www.example.com/?id=2&url=%s",
+      },
+    ],
+  });
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "examplescheme.usesystemdefault",
+    preferredAction: Ci.nsIHandlerInfo.useSystemDefault,
+    alwaysAskBeforeHandling: false,
+    possibleApplicationHandlers: [
+      {
+        name: "Example Possible Handler",
+        uriTemplate: "http://www.example.com/?url=%s",
+      },
+    ],
+  });
+
+  Assert.equal(handlerInfos.length, 0);
+}
+
+/**
+ * Loads data from a file in a predefined format, verifying that the format is
+ * recognized and all the known properties are loaded and saved.
+ */
+add_task(async function test_store_fillHandlerInfo_predefined() {
+  // Test that the file format used in previous versions can be loaded.
+  await copyTestDataToHandlerStore();
+  await assertAllHandlerInfosMatchTestData();
+
+  // Keep a copy of the nsIHandlerInfo instances, then delete the handler store
+  // and populate it with the known data. Since the handler store is empty, the
+  // default handlers for the current locale are also injected, so we have to
+  // delete them manually before adding the other nsIHandlerInfo instances.
+  let testHandlerInfos = HandlerServiceTestUtils.getAllHandlerInfos();
+  await deleteHandlerStore();
+  for (let handlerInfo of HandlerServiceTestUtils.getAllHandlerInfos()) {
+    gHandlerService.remove(handlerInfo);
+  }
+  for (let handlerInfo of testHandlerInfos) {
+    gHandlerService.store(handlerInfo);
+  }
+
+  // Test that the known data still matches after saving it and reloading.
+  await unloadHandlerStore();
+  await assertAllHandlerInfosMatchTestData();
+});
+
+/**
+ * Check that "store" is able to add new instances, that "remove" and "exists"
+ * work, and that "fillHandlerInfo" throws when the instance does not exist.
+ */
+add_task(async function test_store_remove_exists() {
+  // Test both MIME types and protocols.
+  for (let type of [
+    "example/type.usehelperapp",
+    "examplescheme.usehelperapp",
+  ]) {
+    // Create new nsIHandlerInfo instances before loading the test data.
+    await deleteHandlerStore();
+    let handlerInfoPresent = HandlerServiceTestUtils.getHandlerInfo(type);
+    let handlerInfoAbsent = HandlerServiceTestUtils.getHandlerInfo(type + "2");
+
+    // Set up known properties that we can verify later.
+    handlerInfoAbsent.preferredAction = Ci.nsIHandlerInfo.saveToDisk;
+    handlerInfoAbsent.alwaysAskBeforeHandling = false;
+
+    await copyTestDataToHandlerStore();
+
+    Assert.ok(gHandlerService.exists(handlerInfoPresent));
+    Assert.ok(!gHandlerService.exists(handlerInfoAbsent));
+
+    gHandlerService.store(handlerInfoAbsent);
+    gHandlerService.remove(handlerInfoPresent);
+
+    await unloadHandlerStore();
+
+    Assert.ok(!gHandlerService.exists(handlerInfoPresent));
+    Assert.ok(gHandlerService.exists(handlerInfoAbsent));
+
+    Assert.throws(
+      () => gHandlerService.fillHandlerInfo(handlerInfoPresent, ""),
+      ex => ex.result == Cr.NS_ERROR_NOT_AVAILABLE
+    );
+
+    let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo(type + "2");
+    HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+      type: type + "2",
+      preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+      alwaysAskBeforeHandling: false,
+    });
+  }
+});
+
+/**
+ * Tests that it is possible to save an nsIHandlerInfo instance with a
+ * "preferredAction" that is alwaysAsk or has an unknown value, but the
+ * action always becomes useHelperApp when reloading.
+ */
+add_task(async function test_store_preferredAction() {
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+
+  for (let preferredAction of [Ci.nsIHandlerInfo.alwaysAsk, 999]) {
+    handlerInfo.preferredAction = preferredAction;
+    gHandlerService.store(handlerInfo);
+    gHandlerService.fillHandlerInfo(handlerInfo, "");
+    Assert.equal(handlerInfo.preferredAction, Ci.nsIHandlerInfo.useHelperApp);
+  }
+});
+
+/**
+ * Tests that it is possible to save an nsIHandlerInfo instance containing an
+ * nsILocalHandlerApp instance pointing to an executable that doesn't exist, but
+ * this entry is ignored when reloading.
+ */
+add_task(async function test_store_localHandlerApp_missing() {
+  if (!("@mozilla.org/uriloader/dbus-handler-app;1" in Cc)) {
+    info("Skipping test because it does not apply to this platform.");
+    return;
+  }
+
+  let missingHandlerApp = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  missingHandlerApp.name = "Non-existing Handler";
+  missingHandlerApp.executable = FileUtils.getFile("TmpD", ["nonexisting"]);
+
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.preferredApplicationHandler = missingHandlerApp;
+  handlerInfo.possibleApplicationHandlers.appendElement(missingHandlerApp);
+  handlerInfo.possibleApplicationHandlers.appendElement(webHandlerApp);
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    possibleApplicationHandlers: [expectedWebHandlerApp],
+  });
+});
+
+/**
+ * Test saving and reloading an instance of nsIDBusHandlerApp.
+ */
+add_task(async function test_store_dBusHandlerApp() {
+  if (!("@mozilla.org/uriloader/dbus-handler-app;1" in Cc)) {
+    info("Skipping test because it does not apply to this platform.");
+    return;
+  }
+
+  // Set up an nsIDBusHandlerApp instance for testing.
+  let dBusHandlerApp = Cc[
+    "@mozilla.org/uriloader/dbus-handler-app;1"
+  ].createInstance(Ci.nsIDBusHandlerApp);
+  dBusHandlerApp.name = "DBus Handler";
+  dBusHandlerApp.service = "test.method.server";
+  dBusHandlerApp.method = "Method";
+  dBusHandlerApp.dBusInterface = "test.method.Type";
+  dBusHandlerApp.objectPath = "/test/method/Object";
+  let expectedDBusHandlerApp = {
+    name: dBusHandlerApp.name,
+    service: dBusHandlerApp.service,
+    method: dBusHandlerApp.method,
+    dBusInterface: dBusHandlerApp.dBusInterface,
+    objectPath: dBusHandlerApp.objectPath,
+  };
+
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.preferredApplicationHandler = dBusHandlerApp;
+  handlerInfo.possibleApplicationHandlers.appendElement(dBusHandlerApp);
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    preferredApplicationHandler: expectedDBusHandlerApp,
+    possibleApplicationHandlers: [expectedDBusHandlerApp],
+  });
+});
+
+/**
+ * Tests that it is possible to save an nsIHandlerInfo instance with a
+ * "preferredApplicationHandler" and no "possibleApplicationHandlers", but the
+ * former is always included in the latter list when reloading.
+ */
+add_task(
+  async function test_store_possibleApplicationHandlers_includes_preferred() {
+    await deleteHandlerStore();
+
+    let handlerInfo = getKnownHandlerInfo("example/new");
+    handlerInfo.preferredApplicationHandler = localHandlerApp;
+    gHandlerService.store(handlerInfo);
+
+    await unloadHandlerStore();
+
+    let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo(
+      "example/new"
+    );
+    HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+      type: "example/new",
+      preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+      alwaysAskBeforeHandling: false,
+      preferredApplicationHandler: expectedLocalHandlerApp,
+      possibleApplicationHandlers: [expectedLocalHandlerApp],
+    });
+  }
+);
+
+/**
+ * Tests that it is possible to save an nsIHandlerInfo instance with a
+ * "preferredApplicationHandler" that is not the first element in
+ * "possibleApplicationHandlers", but the former is always included as the first
+ * element of the latter list when reloading.
+ */
+add_task(
+  async function test_store_possibleApplicationHandlers_preferred_first() {
+    await deleteHandlerStore();
+
+    let handlerInfo = getKnownHandlerInfo("example/new");
+    handlerInfo.preferredApplicationHandler = webHandlerApp;
+    // The preferred handler is appended after the other one.
+    handlerInfo.possibleApplicationHandlers.appendElement(localHandlerApp);
+    handlerInfo.possibleApplicationHandlers.appendElement(webHandlerApp);
+    gHandlerService.store(handlerInfo);
+
+    await unloadHandlerStore();
+
+    let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo(
+      "example/new"
+    );
+    HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+      type: "example/new",
+      preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+      alwaysAskBeforeHandling: false,
+      preferredApplicationHandler: expectedWebHandlerApp,
+      possibleApplicationHandlers: [
+        expectedWebHandlerApp,
+        expectedLocalHandlerApp,
+      ],
+    });
+  }
+);
+
+/**
+ * Tests that it is possible to save an nsIHandlerInfo instance with an
+ * uppercase file extension, but it is converted to lowercase when reloading.
+ */
+add_task(async function test_store_fileExtensions_lowercase() {
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.appendExtension("extension_test1");
+  handlerInfo.appendExtension("EXTENSION_test2");
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    fileExtensions: ["extension_test1", "extension_test2"],
+  });
+});
+
+/**
+ * Tests that appendExtension doesn't add duplicates, and that anyway duplicates
+ * from possibleApplicationHandlers are removed when saving and reloading.
+ */
+add_task(async function test_store_no_duplicates() {
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.preferredApplicationHandler = webHandlerApp;
+  handlerInfo.possibleApplicationHandlers.appendElement(webHandlerApp);
+  handlerInfo.possibleApplicationHandlers.appendElement(localHandlerApp);
+  handlerInfo.possibleApplicationHandlers.appendElement(localHandlerApp);
+  handlerInfo.possibleApplicationHandlers.appendElement(webHandlerApp);
+  handlerInfo.appendExtension("extension_test1");
+  handlerInfo.appendExtension("extension_test2");
+  handlerInfo.appendExtension("extension_test1");
+  handlerInfo.appendExtension("EXTENSION_test1");
+  Assert.deepEqual(Array.from(handlerInfo.getFileExtensions()), [
+    "extension_test1",
+    "extension_test2",
+  ]);
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    preferredApplicationHandler: expectedWebHandlerApp,
+    possibleApplicationHandlers: [
+      expectedWebHandlerApp,
+      expectedLocalHandlerApp,
+    ],
+    fileExtensions: ["extension_test1", "extension_test2"],
+  });
+});
+
+/**
+ * Tests that setFileExtensions doesn't add duplicates.
+ */
+add_task(async function test_setFileExtensions_no_duplicates() {
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.setFileExtensions("a,b,A,b,c,a");
+  let expected = ["a", "b", "c"];
+  Assert.deepEqual(Array.from(handlerInfo.getFileExtensions()), expected);
+  // Test empty extensions, also at begin and end.
+  handlerInfo.setFileExtensions(",a,,b,A,c,");
+  Assert.deepEqual(Array.from(handlerInfo.getFileExtensions()), expected);
+});
+
+/**
+ * Tests that "store" deletes properties that have their default values from
+ * the data store.
+ *
+ * File extensions are never deleted once they have been associated.
+ */
+add_task(async function test_store_deletes_properties_except_extensions() {
+  await deleteHandlerStore();
+
+  // Prepare an nsIHandlerInfo instance with all the properties set to values
+  // that will result in deletions. The preferredAction is also set to a defined
+  // value so we can more easily verify it later.
+  let handlerInfo = HandlerServiceTestUtils.getBlankHandlerInfo(
+    "example/type.savetodisk"
+  );
+  handlerInfo.preferredAction = Ci.nsIHandlerInfo.saveToDisk;
+  handlerInfo.alwaysAskBeforeHandling = false;
+
+  // All the properties for "example/type.savetodisk" are present in the test
+  // data, so we load the data before overwriting their values.
+  await copyTestDataToHandlerStore();
+  gHandlerService.store(handlerInfo);
+
+  // Now we can reload the data and verify that no extra values have been kept.
+  await unloadHandlerStore();
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo(
+    "example/type.savetodisk"
+  );
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/type.savetodisk",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    fileExtensions: ["example_two", "example_three"],
+  });
+});
+
+/**
+ * Tests the "overrideType" argument of "fillHandlerInfo".
+ */
+add_task(async function test_fillHandlerInfo_overrideType() {
+  // Test both MIME types and protocols.
+  for (let type of [
+    "example/type.usesystemdefault",
+    "examplescheme.usesystemdefault",
+  ]) {
+    await deleteHandlerStore();
+
+    // Create new nsIHandlerInfo instances before loading the test data.
+    let handlerInfoAbsent = HandlerServiceTestUtils.getHandlerInfo(type + "2");
+
+    // Fill the nsIHandlerInfo instance using the type that actually exists.
+    await copyTestDataToHandlerStore();
+    gHandlerService.fillHandlerInfo(handlerInfoAbsent, type);
+    HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfoAbsent, {
+      // While the data is populated from another type, the type is unchanged.
+      type: type + "2",
+      preferredAction: Ci.nsIHandlerInfo.useSystemDefault,
+      alwaysAskBeforeHandling: false,
+      possibleApplicationHandlers: [
+        {
+          name: "Example Possible Handler",
+          uriTemplate: "http://www.example.com/?url=%s",
+        },
+      ],
+    });
+  }
+});
+
+/**
+ * Tests "getTypeFromExtension" including unknown extensions.
+ */
+add_task(async function test_getTypeFromExtension() {
+  await copyTestDataToHandlerStore();
+
+  Assert.equal(gHandlerService.getTypeFromExtension(""), "");
+  Assert.equal(gHandlerService.getTypeFromExtension("example_unknown"), "");
+  Assert.equal(
+    gHandlerService.getTypeFromExtension("example_one"),
+    "example/type.handleinternally"
+  );
+  Assert.equal(
+    gHandlerService.getTypeFromExtension("EXAMPLE_one"),
+    "example/type.handleinternally"
+  );
+});
+
+/**
+ * Checks that the information stored in the handler service instance under
+ * testing matches the default handlers for the English locale.
+ */
+function assertAllHandlerInfosMatchDefaultHandlers() {
+  let handlerInfos = HandlerServiceTestUtils.getAllHandlerInfos();
+
+  for (let type of ["irc", "ircs"]) {
+    HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+      type,
+      preferredActionOSDependent: true,
+      possibleApplicationHandlers: [
+        {
+          name: "Mibbit",
+          uriTemplate: "https://www.mibbit.com/?url=%s",
+        },
+      ],
+    });
+  }
+
+  HandlerServiceTestUtils.assertHandlerInfoMatches(handlerInfos.shift(), {
+    type: "mailto",
+    preferredActionOSDependent: true,
+    possibleApplicationHandlers: [
+      {
+        name: "Yahoo! Mail",
+        uriTemplate: "https://compose.mail.yahoo.com/?To=%s",
+      },
+      {
+        name: "Gmail",
+        uriTemplate: "https://mail.google.com/mail/?extsrc=mailto&url=%s",
+      },
+    ],
+  });
+
+  Assert.equal(handlerInfos.length, 0);
+}
+
+/**
+ * Tests the default protocol handlers imported from the locale-specific data.
+ */
+add_task(async function test_default_protocol_handlers() {
+  if (
+    !Services.prefs.getPrefType("gecko.handlerService.defaultHandlersVersion")
+  ) {
+    info("This platform or locale does not have default handlers.");
+    return;
+  }
+
+  // This will inject the default protocol handlers for the current locale.
+  await deleteHandlerStore();
+
+  await assertAllHandlerInfosMatchDefaultHandlers();
+});
+
+/**
+ * Tests that the default protocol handlers are not imported again from the
+ * locale-specific data if they already exist.
+ */
+add_task(async function test_default_protocol_handlers_no_duplicates() {
+  if (
+    !Services.prefs.getPrefType("gecko.handlerService.defaultHandlersVersion")
+  ) {
+    info("This platform or locale does not have default handlers.");
+    return;
+  }
+
+  // This will inject the default protocol handlers for the current locale.
+  await deleteHandlerStore();
+
+  // Remove the "irc" handler so we can verify that the injection is repeated.
+  let ircHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("irc");
+  gHandlerService.remove(ircHandlerInfo);
+
+  let originalDefaultHandlersVersion = Services.prefs.getComplexValue(
+    "gecko.handlerService.defaultHandlersVersion",
+    Ci.nsIPrefLocalizedString
+  );
+
+  // Set the preference to an arbitrarily high number to force injecting again.
+  Services.prefs.setStringPref(
+    "gecko.handlerService.defaultHandlersVersion",
+    "999"
+  );
+
+  await unloadHandlerStore();
+
+  // Check that "irc" exists to make sure that the injection was repeated.
+  Assert.ok(gHandlerService.exists(ircHandlerInfo));
+
+  // There should be no duplicate handlers in the protocols.
+  await assertAllHandlerInfosMatchDefaultHandlers();
+
+  Services.prefs.setStringPref(
+    "gecko.handlerService.defaultHandlersVersion",
+    originalDefaultHandlersVersion
+  );
+});
+
+/**
+ * Ensures forward compatibility by checking that the "store" method preserves
+ * unknown properties in the test data.
+ */
+add_task(async function test_store_keeps_unknown_properties() {
+  // Create a new nsIHandlerInfo instance before loading the test data.
+  await deleteHandlerStore();
+  let handlerInfo = HandlerServiceTestUtils.getHandlerInfo(
+    "example/type.handleinternally"
+  );
+
+  await copyTestDataToHandlerStore();
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+  let data = JSON.parse(new TextDecoder().decode(await OS.File.read(jsonPath)));
+  Assert.equal(
+    data.mimeTypes["example/type.handleinternally"].unknownProperty,
+    "preserved"
+  );
+});
+
+/**
+ * Runs the asyncInit method, ensuring that it successfully inits the store
+ * and calls the handlersvc-store-initialized topic.
+ */
+add_task(async function test_async_init() {
+  await deleteHandlerStore();
+  await copyTestDataToHandlerStore();
+  gHandlerService.asyncInit();
+  await TestUtils.topicObserved("handlersvc-store-initialized");
+  await assertAllHandlerInfosMatchTestData();
+
+  await unloadHandlerStore();
+});
+
+/**
+ * Races the asyncInit method against the sync init (implicit in enumerate),
+ * to ensure that the store will be synchronously initialized without any
+ * ill effects.
+ */
+add_task(async function test_race_async_init() {
+  await deleteHandlerStore();
+  await copyTestDataToHandlerStore();
+  let storeInitialized = false;
+  // Pass a callback to synchronously observe the topic, as a promise would
+  // resolve asynchronously
+  TestUtils.topicObserved("handlersvc-store-initialized", () => {
+    storeInitialized = true;
+    return true;
+  });
+  gHandlerService.asyncInit();
+  Assert.ok(!storeInitialized);
+  gHandlerService.enumerate();
+  Assert.ok(storeInitialized);
+  await assertAllHandlerInfosMatchTestData();
+
+  await unloadHandlerStore();
+});
+
+/**
+ * Test saving and reloading an instance of nsIGIOMimeApp.
+ */
+add_task(async function test_store_gioHandlerApp() {
+  if (!("@mozilla.org/gio-service;1" in Cc)) {
+    info("Skipping test because it does not apply to this platform.");
+    return;
+  }
+
+  // Create dummy exec file that following won't fail because file not found error
+  let dummyHandlerFile = FileUtils.getFile("TmpD", ["dummyHandler"]);
+  dummyHandlerFile.createUnique(
+    Ci.nsIFile.NORMAL_FILE_TYPE,
+    parseInt("777", 8)
+  );
+
+  // Set up an nsIGIOMimeApp instance for testing.
+  let handlerApp = Cc["@mozilla.org/gio-service;1"]
+    .getService(Ci.nsIGIOService)
+    .createAppFromCommand(dummyHandlerFile.path, "Dummy GIO handler");
+  let expectedGIOMimeHandlerApp = {
+    name: handlerApp.name,
+    command: handlerApp.command,
+  };
+
+  await deleteHandlerStore();
+
+  let handlerInfo = getKnownHandlerInfo("example/new");
+  handlerInfo.preferredApplicationHandler = handlerApp;
+  handlerInfo.possibleApplicationHandlers.appendElement(handlerApp);
+  handlerInfo.possibleApplicationHandlers.appendElement(webHandlerApp);
+  gHandlerService.store(handlerInfo);
+
+  await unloadHandlerStore();
+
+  let actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    preferredApplicationHandler: expectedGIOMimeHandlerApp,
+    possibleApplicationHandlers: [expectedGIOMimeHandlerApp, webHandlerApp],
+  });
+
+  await OS.File.remove(dummyHandlerFile.path);
+
+  // After removing dummyHandlerFile, the handler should disappear from the
+  // list of possibleApplicationHandlers and preferredAppHandler should be null.
+  actualHandlerInfo = HandlerServiceTestUtils.getHandlerInfo("example/new");
+  HandlerServiceTestUtils.assertHandlerInfoMatches(actualHandlerInfo, {
+    type: "example/new",
+    preferredAction: Ci.nsIHandlerInfo.saveToDisk,
+    alwaysAskBeforeHandling: false,
+    preferredApplicationHandler: null,
+    possibleApplicationHandlers: [webHandlerApp],
+  });
+});
diff --git a/uriloader/exthandler/tests/unit/test_protocol_ask_dialog_telemetry.js b/uriloader/exthandler/tests/unit/test_protocol_ask_dialog_telemetry.js
new file mode 100644
index 0000000000..161cce8d33
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_protocol_ask_dialog_telemetry.js
@@ -0,0 +1,117 @@
+/* Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const { ContentDispatchChooserTelemetry } = ChromeUtils.import(
+  "resource://gre/modules/ContentDispatchChooser.jsm"
+);
+
+let telemetryLabels = Services.telemetry.getCategoricalLabels()
+  .EXTERNAL_PROTOCOL_HANDLER_DIALOG_CONTEXT_SCHEME;
+
+let schemeToLabel = ContentDispatchChooserTelemetry.SCHEME_TO_LABEL;
+let schemePrefixToLabel =
+  ContentDispatchChooserTelemetry.SCHEME_PREFIX_TO_LABEL;
+
+/**
+ * Test for scheme-label mappings of protocol ask dialog telemetry.
+ */
+add_task(async function test_telemetry_label_maps() {
+  let mapValues = Object.values(schemeToLabel).concat(
+    Object.values(schemePrefixToLabel)
+  );
+
+  // Scheme - label maps must have valid label values.
+  mapValues.forEach(label => {
+    // Mapped labels must be valid.
+    Assert.ok(telemetryLabels.includes(label), `Exists label: ${label}`);
+  });
+
+  // Uppercase labels must have a mapping.
+  telemetryLabels.forEach(label => {
+    Assert.equal(
+      label == "OTHER" || mapValues.includes(label),
+      label == label.toUpperCase(),
+      `Exists label: ${label}`
+    );
+  });
+
+  Object.keys(schemeToLabel).forEach(key => {
+    // Schemes which have a mapping must not exist as as label.
+    Assert.ok(!telemetryLabels.includes(key), `Not exists label: ${key}`);
+
+    // There must be no key duplicates across the two maps.
+    Assert.ok(!schemePrefixToLabel[key], `No duplicate key: ${key}`);
+  });
+});
+
+/**
+ * Tests the getTelemetryLabel method.
+ */
+add_task(async function test_telemetry_getTelemetryLabel() {
+  // Method should return the correct mapping.
+  Object.keys(schemeToLabel).forEach(scheme => {
+    Assert.equal(
+      schemeToLabel[scheme],
+      ContentDispatchChooserTelemetry._getTelemetryLabel(scheme)
+    );
+  });
+
+  // Passing null to _getTelemetryLabel should throw.
+  Assert.throws(() => {
+    ContentDispatchChooserTelemetry._getTelemetryLabel(null);
+  }, /Invalid scheme/);
+
+  // Replace maps with test data
+  ContentDispatchChooserTelemetry.SCHEME_TO_LABEL = {
+    foo: "FOOLABEL",
+    bar: "BARLABEL",
+  };
+
+  ContentDispatchChooserTelemetry.SCHEME_PREFIX_TO_LABEL = {
+    fooPrefix: "FOOPREFIXLABEL",
+    barPrefix: "BARPREFIXLABEL",
+    fo: "PREFIXLABEL",
+  };
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("foo"),
+    "FOOLABEL",
+    "Non prefix mapping should have priority"
+  );
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("bar"),
+    "BARLABEL",
+    "Should return the correct label"
+  );
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("fooPrefix"),
+    "FOOPREFIXLABEL",
+    "Should return the correct label"
+  );
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("fooPrefix1"),
+    "FOOPREFIXLABEL",
+    "Should return the correct label"
+  );
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("fooPrefix2"),
+    "FOOPREFIXLABEL",
+    "Should return the correct label"
+  );
+
+  Assert.equal(
+    ContentDispatchChooserTelemetry._getTelemetryLabel("doesnotexist"),
+    "OTHER",
+    "Should return the correct label for unknown scheme"
+  );
+
+  // Restore maps
+  ContentDispatchChooserTelemetry.SCHEME_TO_LABEL = schemeToLabel;
+  ContentDispatchChooserTelemetry.SCHEME_PREFIX_TO_LABEL = schemePrefixToLabel;
+});
diff --git a/uriloader/exthandler/tests/unit/test_punycodeURIs.js b/uriloader/exthandler/tests/unit/test_punycodeURIs.js
new file mode 100644
index 0000000000..638128d11b
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/test_punycodeURIs.js
@@ -0,0 +1,130 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// Encoded test URI to work on all platforms/independent of file encoding
+const kTestURI = "http://\u65e5\u672c\u8a93.jp/";
+const kExpectedURI = "http://xn--wgv71a309e.jp/";
+const kOutputFile = "result.txt";
+
+// Try several times in case the box we're running on is slow.
+const kMaxCheckExistAttempts = 30; // seconds
+var gCheckExistsAttempts = 0;
+
+const tempDir = do_get_tempdir();
+
+function checkFile() {
+  // This is where we expect the output
+  var tempFile = tempDir.clone();
+  tempFile.append(kOutputFile);
+
+  if (!tempFile.exists()) {
+    if (gCheckExistsAttempts >= kMaxCheckExistAttempts) {
+      do_throw(
+        "Expected File " +
+          tempFile.path +
+          " does not exist after " +
+          kMaxCheckExistAttempts +
+          " seconds"
+      );
+    } else {
+      ++gCheckExistsAttempts;
+      // Wait a bit longer then try again
+      do_timeout(1000, checkFile);
+      return;
+    }
+  }
+
+  // Now read it
+  var fstream = Cc["@mozilla.org/network/file-input-stream;1"].createInstance(
+    Ci.nsIFileInputStream
+  );
+  var sstream = Cc["@mozilla.org/scriptableinputstream;1"].createInstance(
+    Ci.nsIScriptableInputStream
+  );
+  fstream.init(tempFile, -1, 0, 0);
+  sstream.init(fstream);
+
+  // Read the first line only as that's the one we expect WriteArguments
+  // to be writing the argument to.
+  var data = sstream.read(4096);
+
+  sstream.close();
+  fstream.close();
+
+  // Now remove the old file
+  tempFile.remove(false);
+
+  // This currently fails on Mac with an argument like -psn_0_nnnnnn
+  // This seems to be to do with how the executable is called, but I couldn't
+  // find a way around it.
+  // Additionally the lack of OS detection in xpcshell tests sucks, so we'll
+  // have to check for the argument mac gives us.
+  if (data.substring(0, 7) != "-psn_0_") {
+    Assert.equal(data, kExpectedURI);
+  }
+
+  do_test_finished();
+}
+
+function run_test() {
+  if (mozinfo.os == "mac") {
+    dump("INFO | test_punycodeURIs.js | Skipping test on mac, bug 599475");
+    return;
+  }
+
+  // set up the uri to test with
+  var ioService = Services.io;
+
+  // set up the local handler object
+  var localHandler = Cc[
+    "@mozilla.org/uriloader/local-handler-app;1"
+  ].createInstance(Ci.nsILocalHandlerApp);
+  localHandler.name = "Test Local Handler App";
+
+  // WriteArgument will just dump its arguments to a file for us.
+  var processDir = do_get_cwd();
+  var exe = processDir.clone();
+  exe.append("WriteArgument");
+
+  if (!exe.exists()) {
+    // Maybe we are on windows
+    exe.leafName = "WriteArgument.exe";
+    if (!exe.exists()) {
+      do_throw("Could not locate the WriteArgument tests executable\n");
+    }
+  }
+
+  var outFile = tempDir.clone();
+  outFile.append(kOutputFile);
+
+  // Set an environment variable for WriteArgument to pick up
+  var envSvc = Cc["@mozilla.org/process/environment;1"].getService(
+    Ci.nsIEnvironment
+  );
+
+  // The Write Argument file needs to know where its libraries are, so
+  // just force the path variable
+  // For mac
+  var greDir = Services.dirsvc.get("GreD", Ci.nsIFile);
+
+  envSvc.set("DYLD_LIBRARY_PATH", greDir.path);
+  // For Linux
+  envSvc.set("LD_LIBRARY_PATH", greDir.path);
+  // XXX: handle windows
+
+  // Now tell it where we want the file.
+  envSvc.set("WRITE_ARGUMENT_FILE", outFile.path);
+
+  var uri = ioService.newURI(kTestURI);
+
+  // Just check we've got these matching, if we haven't there's a problem
+  // with ascii spec or our test case.
+  Assert.equal(uri.asciiSpec, kExpectedURI);
+
+  localHandler.executable = exe;
+  localHandler.launchWithURI(uri);
+
+  do_test_pending();
+  do_timeout(1000, checkFile);
+}
diff --git a/uriloader/exthandler/tests/unit/xpcshell.ini b/uriloader/exthandler/tests/unit/xpcshell.ini
new file mode 100644
index 0000000000..d7bf9e54d6
--- /dev/null
+++ b/uriloader/exthandler/tests/unit/xpcshell.ini
@@ -0,0 +1,28 @@
+[DEFAULT]
+head = head.js
+run-sequentially = Bug 912235 - Intermittent failures
+firefox-appdir = browser
+
+[test_defaults_handlerService.js]
+# No default stored handlers on android given lack of support.
+# No default stored handlers on Thunderbird.
+skip-if = os == "android" || appname == "thunderbird"
+[test_getMIMEInfo_pdf.js]
+[test_getMIMEInfo_unknown_mime_type.js]
+run-if = os == "win" # Windows only test
+[test_getTypeFromExtension_ext_to_type_mapping.js]
+[test_getTypeFromExtension_with_empty_Content_Type.js]
+run-if = os == "win" # Windows only test
+[test_badMIMEType.js]
+[test_handlerService.js]
+skip-if = (verify && (os == 'win'))
+support-files = mailcap
+# Bug 676997: test consistently fails on Android
+fail-if = os == "android"
+[test_handlerService_store.js]
+# Disabled for 1563343 -- the app should determine possible handlers in GV.
+fail-if = os == "android"
+support-files = handlers.json
+[test_punycodeURIs.js]
+[test_protocol_ask_dialog_telemetry.js]
+skip-if = os == "android" # Desktop telemetry