--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -298,43 +298,61 @@ GeckoDriver.prototype.sendTargettedAsync
 
       default:
         throw new WebDriverError(e);
     }
   }
 };
 
 /**
- * Gets the current active window.
+ * Get the session's current top-level browsing context.
+ *
+ * It will return the outer {@ChromeWindow} previously selected by window handle
+ * through {@code #switchToWindow}, or the first window that was registered.
  *
  * @param {Context=} forcedContext
- *     Optional name of the context to use for the checks.
- *     Defaults to the current context.
+ *     Optional name of the context to use for finding the window. It will be required
+ *     if a command always needs a specific context, whether which context is
+ *     currently set. Defaults to the current context.
  *
- * @return {nsIDOMWindow}
+ * @return {ChromeWindow}
+ *     The current top-level browsing context.
  */
 GeckoDriver.prototype.getCurrentWindow = function (forcedContext = undefined) {
   let context = typeof forcedContext == "undefined" ? this.context : forcedContext;
   let win = null;
 
-  if (this.curFrame === null) {
-    if (this.curBrowser === null) {
-      let typ = (context === Context.CONTENT) ? "navigator:browser" : null;
-      win = Services.wm.getMostRecentWindow(typ);
-    } else {
-      if (context === Context.CHROME) {
+  switch (context) {
+    case Context.CHROME:
+      if (this.curFrame !== null) {
+        win = this.curFrame;
+
+      } else if (this.curBrowser !== null) {
         win = this.curBrowser.window;
-      } else {
-        if (this.curBrowser.tab && browser.getBrowserForTab(this.curBrowser.tab)) {
+      }
+
+      break;
+
+    case Context.CONTENT:
+      if (this.curFrame !== null) {
+        win = this.curFrame;
+
+      } else if (this.curBrowser !== null) {
+        if (browser.getTabBrowser(this.curBrowser.window)) {
+          // For browser windows we have to check if the current tab still exists.
+          if (this.curBrowser.tab && browser.getBrowserForTab(this.curBrowser.tab)) {
+            win = this.curBrowser.window;
+          }
+        } else {
+          // For non-browser windows just return the window.
           win = this.curBrowser.window;
         }
       }
-    }
-  } else {
-    win = this.curFrame;
+
+      break;
   }
 
   return win;
 };
 
 GeckoDriver.prototype.addFrameCloseListener = function (action) {
   let win = this.getCurrentWindow();
   this.mozBrowserClose = e => {
@@ -593,17 +611,17 @@ GeckoDriver.prototype.newSession = funct
   if (this.a11yChecks && accessibility.service) {
     logger.info("Preemptively starting accessibility service in Chrome");
   }
 
   let registerBrowsers = this.registerPromise();
   let browserListening = this.listeningPromise();
 
   let waitForWindow = function() {
-    let win = this.getCurrentWindow();
+    let win = Services.wm.getMostRecentWindow("navigator:browser");
     if (!win) {
       // if the window isn't even created, just poll wait for it
       let checkTimer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
       checkTimer.initWithCallback(waitForWindow.bind(this), 100,
           Ci.nsITimer.TYPE_ONE_SHOT);
     } else if (win.document.readyState != "complete") {
       // otherwise, wait for it to be fully loaded before proceeding
       let listener = ev => {
@@ -613,20 +631,18 @@ GeckoDriver.prototype.newSession = funct
           return;
         }
         win.removeEventListener("load", listener);
         waitForWindow.call(this);
       };
       win.addEventListener("load", listener, true);
     } else {
       let clickToStart = Preferences.get(CLICK_TO_START_PREF);
-      if (clickToStart && (this.appName != "B2G")) {
-        let pService = Cc["@mozilla.org/embedcomp/prompt-service;1"]
-            .getService(Ci.nsIPromptService);
-        pService.alert(win, "", "Click to start execution of marionette tests");
+      if (clickToStart) {
+        Services.prompt.alert(win, "", "Click to start execution of marionette tests");
       }
       this.startBrowser(win, true);
     }
   };
 
   if (!Preferences.get(CONTENT_LISTENER_PREF)) {
     waitForWindow.call(this);
   } else if (this.appName != "Firefox" && this.curBrowser === null) {

--- a/testing/marionette/harness/marionette_harness/tests/unit/test_window_handles_content.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_window_handles_content.py
@@ -1,15 +1,15 @@
 # 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/.
 
 from marionette_driver import By, Wait
 
-from marionette_harness import MarionetteTestCase, WindowManagerMixin
+from marionette_harness import MarionetteTestCase, skip_if_mobile, WindowManagerMixin
 
 
 class TestWindowHandles(WindowManagerMixin, MarionetteTestCase):
 
     def setUp(self):
         super(TestWindowHandles, self).setUp()
 
         self.empty_page = self.marionette.absolute_url("empty.html")
@@ -42,17 +42,17 @@ class TestWindowHandles(WindowManagerMix
 
         self.marionette.switch_to_window(new_tab)
         self.marionette.close()
         self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs))
 
         self.marionette.switch_to_window(self.start_tab)
         self.assertEqual(self.marionette.current_window_handle, self.start_tab)
 
-    def test_window_handles_after_opening_new_window(self):
+    def test_window_handles_after_opening_new_browser_window(self):
         def open_with_link():
             link = self.marionette.find_element(By.ID, "new-window")
             link.click()
 
         # We open a new window but are actually interested in the new tab
         new_tab = self.open_tab(trigger=open_with_link)
         self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs) + 1)
         self.assertEqual(self.marionette.current_window_handle, self.start_tab)
@@ -72,16 +72,38 @@ class TestWindowHandles(WindowManagerMix
         # Close the opened window and carry on in our original tab.
         self.marionette.close()
         self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs))
 
         self.marionette.switch_to_window(self.start_tab)
         self.assertEqual(self.marionette.current_window_handle, self.start_tab)
         self.assertEqual(self.marionette.get_url(), self.test_page)
 
+    @skip_if_mobile("Fennec doesn't support other chrome windows")
+    def test_window_handles_after_opening_new_non_browser_window(self):
+        def open_with_link():
+            self.marionette.navigate(self.marionette.absolute_url("blob_download.html"))
+            link = self.marionette.find_element(By.ID, "blob-download")
+            link.click()
+
+        # We open a new window but are actually interested in the new tab
+        new_tab = self.open_tab(trigger=open_with_link)
+        self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs) + 1)
+        self.assertEqual(self.marionette.current_window_handle, self.start_tab)
+
+        self.marionette.switch_to_window(new_tab)
+        self.assertEqual(self.marionette.current_window_handle, new_tab)
+
+        # Close the opened window and carry on in our original tab.
+        self.marionette.close()
+        self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs))
+
+        self.marionette.switch_to_window(self.start_tab)
+        self.assertEqual(self.marionette.current_window_handle, self.start_tab)
+
     def test_window_handles_after_closing_original_tab(self):
         def open_with_link():
             link = self.marionette.find_element(By.ID, "new-tab")
             link.click()
 
         new_tab = self.open_tab(trigger=open_with_link)
         self.assertEqual(len(self.marionette.window_handles), len(self.start_tabs) + 1)
         self.assertEqual(self.marionette.current_window_handle, self.start_tab)

--- a/testing/marionette/harness/marionette_harness/tests/unit/test_window_management.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_window_management.py
@@ -9,17 +9,17 @@ from marionette_harness import Marionett
 
 
 class TestNoSuchWindowContent(WindowManagerMixin, MarionetteTestCase):
 
     def setUp(self):
         super(TestNoSuchWindowContent, self).setUp()
 
     def tearDown(self):
-        self.close_all_windows()
+        self.close_all_tabs()
         super(TestNoSuchWindowContent, self).tearDown()
 
     @skip_if_mobile("Fennec doesn't support other chrome windows")
     def test_closed_chrome_window(self):
 
         def open_with_link():
             with self.marionette.using_context("content"):
                 test_page = self.marionette.absolute_url("windowHandles.html")

new file mode 100644
--- /dev/null
+++ b/testing/marionette/harness/marionette_harness/www/blob_download.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+
+<a id="blob-download" download="foo.html">Download</a>
+
+<script>
+  const string = "test";
+  const blob = new Blob([string], { type: "text/html" });
+
+  const link = document.getElementById("blob-download");
+  link.href = URL.createObjectURL(blob);
+</script>