diff --git a/uriloader/exthandler/tests/mochitest/browser.ini b/uriloader/exthandler/tests/mochitest/browser.ini
index 9647dcf8cd00..a1de09e185d8 100644
--- a/uriloader/exthandler/tests/mochitest/browser.ini
+++ b/uriloader/exthandler/tests/mochitest/browser.ini
@@ -1,8 +1,12 @@
 [DEFAULT]
 head = head.js
 support-files =
+  download_page.html
+  download.bin
   protocolHandler.html
 
+[browser_auto_close_window.js]
+skip-if = !e10s # test relies on e10s behavior
 [browser_download_always_ask_preferred_app.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 000000000000..32f0e8e2eb61
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/browser_auto_close_window.js
@@ -0,0 +1,103 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const URL =
+  getRootDirectory(gTestPath).replace("chrome://mochitests/content",
+                                      "https://example.com") +
+    "download_page.html";
+
+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: function(aLauncher, aWindowContext, aReason) {
+    ok(true, "Showing the helper app dialog");
+    curDialogResolve(aWindowContext);
+    executeSoon(() => { aLauncher.cancel(Cr.NS_ERROR_ABORT); });
+  },
+  QueryInterface: XPCOMUtils.generateQI([Ci.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 = XPCOMUtils._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: URL }, function* (browser) {
+    let dialogAppeared = promiseHelperAppDialog();
+    yield BrowserTestUtils.synthesizeMouseAtCenter("#regular_load", {}, browser);
+    let windowContext = yield dialogAppeared;
+
+    is(windowContext.gBrowser.selectedBrowser.currentURI.spec, URL,
+       "got the right windowContext");
+  });
+});
+
+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: URL }, function* (browser) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let tabOpened = BrowserTestUtils.waitForEvent(gBrowser.tabContainer, "TabOpen").then((event) => {
+      return event.target;
+    });
+
+    yield BrowserTestUtils.synthesizeMouseAtCenter("#target_blank", {}, browser);
+
+    let windowContext = yield dialogAppeared;
+    is(windowContext.gBrowser.selectedBrowser.currentURI.spec, URL,
+       "got the right windowContext");
+    let tab = yield tabOpened;
+    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: URL }, function* (browser) {
+    let dialogAppeared = promiseHelperAppDialog();
+    let windowOpened = BrowserTestUtils.waitForNewWindow(false);
+
+    yield BrowserTestUtils.synthesizeMouseAtCenter("#new_window", {}, browser);
+
+    let windowContext = yield dialogAppeared;
+    is(windowContext.gBrowser.selectedBrowser.currentURI.spec, URL,
+       "got the right windowContext");
+    let win = yield windowOpened;
+    is(win.closed, true, "window was opened and closed");
+  });
+});
+
+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/download.bin b/uriloader/exthandler/tests/mochitest/download.bin
new file mode 100644
index 000000000000..0e4b0c7bae67
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/download.bin
@@ -0,0 +1 @@
+abc123
diff --git a/uriloader/exthandler/tests/mochitest/download_page.html b/uriloader/exthandler/tests/mochitest/download_page.html
new file mode 100644
index 000000000000..3f482cd238ab
--- /dev/null
+++ b/uriloader/exthandler/tests/mochitest/download_page.html
@@ -0,0 +1,18 @@
+<!-- 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; version=1.8">
+    function launch_download() {
+      window.open("download.bin", "_blank", "height=100,width=100");
+    }
+  </script>
+</head>
+<body>
+  <a href="download.bin" id="regular_load">regular load</a>
+  <a href="download.bin" id="target_blank" target="_blank">target blank</a>
+  <a href="#" onclick="launch_download(); return false" id="new_window">new window</a>
+</body>