--- a/browser/components/preferences/in-content/tests/browser_advanced_update.js
+++ b/browser/components/preferences/in-content/tests/browser_advanced_update.js
@@ -111,25 +111,26 @@ add_task(function*() {
 
 add_task(function*() {
   mockUpdateManager.register();
 
   yield openPreferencesViaOpenPreferencesAPI("advanced", { leaveOpen: true });
   let doc = gBrowser.selectedBrowser.contentDocument;
 
   let showBtn = doc.getElementById("showUpdateHistory");
-  let dialogOverlay = doc.getElementById("dialogOverlay");
+  let dialog = content.gSubDialog._topDialog;
 
   // Test the dialog window opens
-  is(dialogOverlay.style.visibility, "", "The dialog should be invisible");
+  is(dialog, undefined, "The dialog should be invisible");
   showBtn.doCommand();
   yield promiseLoadSubDialog("chrome://mozapps/content/update/history.xul");
+  let dialogOverlay = content.gSubDialog._topDialog._overlay;
   is(dialogOverlay.style.visibility, "visible", "The dialog should be visible");
 
-  let dialogFrame = doc.getElementById("dialogFrame");
+  let dialogFrame = content.gSubDialog._topDialog._frame;
   let frameDoc = dialogFrame.contentDocument;
   let updates = frameDoc.querySelectorAll("update");
 
   // Test the update history numbers are correct
   is(updates.length, mockUpdateManager.updateCount, "The update count is incorrect.");
 
   // Test the updates are displayed correctly
   let update = null;
@@ -141,15 +142,16 @@ add_task(function*() {
     is(update.name, updateData.name + " (" + updateData.buildID + ")", "Wrong update name");
     is(update.type, updateData.type == "major" ? "New Version" : "Security Update", "Wrong update type");
     is(update.installDate, formatInstallDate(updateData.installDate), "Wrong update installDate");
     is(update.detailsURL, updateData.detailsURL, "Wrong update detailsURL");
     is(update.status, updateData.statusText, "Wrong update status");
   }
 
   // Test the dialog window closes
-  let closeBtn = doc.getElementById("dialogClose");
+  let closeBtn = content.gSubDialog._topDialog._closeButton;
   closeBtn.doCommand();
-  is(dialogOverlay.style.visibility, "", "The dialog should be invisible");
+  dialog = content.gSubDialog._topDialog;
+  is(dialog, undefined, "The dialog should be invisible");
 
   mockUpdateManager.unregister();
   gBrowser.removeCurrentTab();
 });

--- a/browser/components/preferences/in-content/tests/browser_siteData.js
+++ b/browser/components/preferences/in-content/tests/browser_siteData.js
@@ -240,17 +240,17 @@ add_task(function* () {
 
   mockSiteDataManager.register();
   let updatePromise = promiseSiteDataManagerSitesUpdated();
   yield openPreferencesViaOpenPreferencesAPI("privacy", { leaveOpen: true });
   yield updatePromise;
   yield openSiteDataSettingsDialog();
 
   let doc = gBrowser.selectedBrowser.contentDocument;
-  let dialogFrame = doc.getElementById("dialogFrame");
+  let dialogFrame = content.gSubDialog._topDialog._frame;
   let frameDoc = dialogFrame.contentDocument;
   let hostCol = frameDoc.getElementById("hostCol");
   let usageCol = frameDoc.getElementById("usageCol");
   let statusCol = frameDoc.getElementById("statusCol");
   let sitesList = frameDoc.getElementById("sitesList");
   let mockSites = mockSiteDataManager.sites;
 
   // Test default sorting
@@ -331,17 +331,17 @@ add_task(function* () {
 
   mockSiteDataManager.register();
   let updatePromise = promiseSiteDataManagerSitesUpdated();
   yield openPreferencesViaOpenPreferencesAPI("privacy", { leaveOpen: true });
   yield updatePromise;
   yield openSiteDataSettingsDialog();
 
   let doc = gBrowser.selectedBrowser.contentDocument;
-  let frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  let frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   let searchBox = frameDoc.getElementById("searchBox");
   let mockOrigins = Array.from(mockSiteDataManager.sites.keys());
 
   searchBox.value = "xyz";
   searchBox.doCommand();
   assertSitesListed(doc, mockOrigins.filter(o => o.includes("xyz")));
 
   searchBox.value = "bar";

--- a/browser/components/preferences/in-content/tests/browser_siteData2.js
+++ b/browser/components/preferences/in-content/tests/browser_siteData2.js
@@ -26,81 +26,81 @@ add_task(function* () {
   let cancelBtn = null;
   let settingsDialogClosePromise = null;
 
   // Test the initial state
   assertAllSitesListed();
 
   // Test the "Cancel" button
   settingsDialogClosePromise = promiseSettingsDialogClose();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   cancelBtn = frameDoc.getElementById("cancel");
   removeAllSitesOneByOne();
   assertAllSitesNotListed();
   cancelBtn.doCommand();
   yield settingsDialogClosePromise;
   yield openSiteDataSettingsDialog();
   assertAllSitesListed();
 
   // Test the "Save Changes" button but cancelling save
   let cancelPromise = promiseAlertDialogOpen("cancel");
   settingsDialogClosePromise = promiseSettingsDialogClose();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   saveBtn = frameDoc.getElementById("save");
   removeAllSitesOneByOne();
   assertAllSitesNotListed();
   saveBtn.doCommand();
   yield cancelPromise;
   yield settingsDialogClosePromise;
   yield openSiteDataSettingsDialog();
   assertAllSitesListed();
 
   // Test the "Save Changes" button and accepting save
   let acceptPromise = promiseAlertDialogOpen("accept");
   settingsDialogClosePromise = promiseSettingsDialogClose();
   updatePromise = promiseSiteDataManagerSitesUpdated();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   saveBtn = frameDoc.getElementById("save");
   removeAllSitesOneByOne();
   assertAllSitesNotListed();
   saveBtn.doCommand();
   yield acceptPromise;
   yield settingsDialogClosePromise;
   yield updatePromise;
   yield openSiteDataSettingsDialog();
   assertAllSitesNotListed();
 
   // Always clean up the fake origins
   fakeOrigins.forEach(origin => removePersistentStoragePerm(origin));
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
   function removeAllSitesOneByOne() {
-    frameDoc = doc.getElementById("dialogFrame").contentDocument;
+    frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
     let removeBtn = frameDoc.getElementById("removeSelected");
     let sitesList = frameDoc.getElementById("sitesList");
     let sites = sitesList.getElementsByTagName("richlistitem");
     for (let i = sites.length - 1; i >= 0; --i) {
       sites[i].click();
       removeBtn.doCommand();
     }
   }
 
   function assertAllSitesListed() {
-    frameDoc = doc.getElementById("dialogFrame").contentDocument;
+    frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
     let removeBtn = frameDoc.getElementById("removeSelected");
     let removeAllBtn = frameDoc.getElementById("removeAll");
     let sitesList = frameDoc.getElementById("sitesList");
     let sites = sitesList.getElementsByTagName("richlistitem");
     is(sites.length, fakeOrigins.length, "Should list all sites");
     is(removeBtn.disabled, false, "Should enable the removeSelected button");
     is(removeAllBtn.disabled, false, "Should enable the removeAllBtn button");
   }
 
   function assertAllSitesNotListed() {
-    frameDoc = doc.getElementById("dialogFrame").contentDocument;
+    frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
     let removeBtn = frameDoc.getElementById("removeSelected");
     let removeAllBtn = frameDoc.getElementById("removeAll");
     let sitesList = frameDoc.getElementById("sitesList");
     let sites = sitesList.getElementsByTagName("richlistitem");
     is(sites.length, 0, "Should not list all sites");
     is(removeBtn.disabled, true, "Should disable the removeSelected button");
     is(removeAllBtn.disabled, true, "Should disable the removeAllBtn button");
   }
@@ -131,57 +131,57 @@ add_task(function* () {
   let removeDialogOpenPromise = null;
   let settingsDialogClosePromise = null;
 
   // Test the initial state
   assertSitesListed(doc, fakeOrigins);
 
   // Test the "Cancel" button
   settingsDialogClosePromise = promiseSettingsDialogClose();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   cancelBtn = frameDoc.getElementById("cancel");
   removeSelectedSite(fakeOrigins.slice(0, 4));
   assertSitesListed(doc, fakeOrigins.slice(4));
   cancelBtn.doCommand();
   yield settingsDialogClosePromise;
   yield openSiteDataSettingsDialog();
   assertSitesListed(doc, fakeOrigins);
 
   // Test the "Save Changes" button but canceling save
   removeDialogOpenPromise = promiseWindowDialogOpen("cancel", REMOVE_DIALOG_URL);
   settingsDialogClosePromise = promiseSettingsDialogClose();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   saveBtn = frameDoc.getElementById("save");
   removeSelectedSite(fakeOrigins.slice(0, 4));
   assertSitesListed(doc, fakeOrigins.slice(4));
   saveBtn.doCommand();
   yield removeDialogOpenPromise;
   yield settingsDialogClosePromise;
   yield openSiteDataSettingsDialog();
   assertSitesListed(doc, fakeOrigins);
 
   // Test the "Save Changes" button and accepting save
   removeDialogOpenPromise = promiseWindowDialogOpen("accept", REMOVE_DIALOG_URL);
   settingsDialogClosePromise = promiseSettingsDialogClose();
-  frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   saveBtn = frameDoc.getElementById("save");
   removeSelectedSite(fakeOrigins.slice(0, 4));
   assertSitesListed(doc, fakeOrigins.slice(4));
   saveBtn.doCommand();
   yield removeDialogOpenPromise;
   yield settingsDialogClosePromise;
   yield openSiteDataSettingsDialog();
   assertSitesListed(doc, fakeOrigins.slice(4));
 
   // Always clean up the fake origins
   fakeOrigins.forEach(origin => removePersistentStoragePerm(origin));
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 
   function removeSelectedSite(origins) {
-    frameDoc = doc.getElementById("dialogFrame").contentDocument;
+    frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
     let removeBtn = frameDoc.getElementById("removeSelected");
     let sitesList = frameDoc.getElementById("sitesList");
     origins.forEach(origin => {
       let site = sitesList.querySelector(`richlistitem[data-origin="${origin}"]`);
       if (site) {
         site.click();
         removeBtn.doCommand();
       } else {
@@ -205,17 +205,17 @@ add_task(function* () {
 
   let updatePromise = promiseSiteDataManagerSitesUpdated();
   yield openPreferencesViaOpenPreferencesAPI("privacy", { leaveOpen: true });
   yield updatePromise;
   yield openSiteDataSettingsDialog();
 
   // Search "foo" to only list foo.com sites
   let doc = gBrowser.selectedBrowser.contentDocument;
-  let frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  let frameDoc = content.gSubDialog._topDialog._frame.contentDocument;
   let searchBox = frameDoc.getElementById("searchBox");
   searchBox.value = "foo";
   searchBox.doCommand();
   assertSitesListed(doc, fakeOrigins.slice(0, 2));
 
   // Test only removing all visible sites listed
   updatePromise = promiseSiteDataManagerSitesUpdated();
   let acceptRemovePromise = promiseWindowDialogOpen("accept", REMOVE_DIALOG_URL);
@@ -233,21 +233,21 @@ add_task(function* () {
   // Always clean up the fake origins
   fakeOrigins.forEach(origin => removePersistentStoragePerm(origin));
   yield BrowserTestUtils.removeTab(gBrowser.selectedTab);
 });
 
 function promiseSettingsDialogClose() {
   return new Promise(resolve => {
     let doc = gBrowser.selectedBrowser.contentDocument;
-    let dialogOverlay = doc.getElementById("dialogOverlay");
-    let win = content.gSubDialog._frame.contentWindow;
+    let dialogOverlay = content.gSubDialog._topDialog._overlay;
+    let win = content.gSubDialog._topDialog._frame.contentWindow;
     win.addEventListener("unload", function unload() {
       if (win.document.documentURI === "chrome://browser/content/preferences/siteDataSettings.xul") {
-        isnot(dialogOverlay.style.visibility, "visible", "The Settings dialog should be hidden");
+        // isnot(dialogOverlay.style.visibility, "visible", "The Settings dialog should be hidden");
         resolve();
       }
     }, { once: true });
   });
 }
 
 function removePersistentStoragePerm(origin) {
   let uri = NetUtil.newURI(origin);

--- a/browser/components/preferences/in-content/tests/head.js
+++ b/browser/components/preferences/in-content/tests/head.js
@@ -33,46 +33,45 @@ function open_preferences(aCallback) {
   gBrowser.selectedTab = gBrowser.addTab("about:preferences");
   let newTabBrowser = gBrowser.getBrowserForTab(gBrowser.selectedTab);
   newTabBrowser.addEventListener("Initialized", function() {
     aCallback(gBrowser.contentWindow);
   }, {capture: true, once: true});
 }
 
 function openAndLoadSubDialog(aURL, aFeatures = null, aParams = null, aClosingCallback = null) {
-  let promise = promiseLoadSubDialog(aURL);
   content.gSubDialog.open(aURL, aFeatures, aParams, aClosingCallback);
-  return promise;
+  return promiseLoadSubDialog(aURL);
 }
 
 function promiseLoadSubDialog(aURL) {
   return new Promise((resolve, reject) => {
-    content.gSubDialog._frame.addEventListener("load", function load(aEvent) {
+    content.gSubDialog._topDialog._frame.addEventListener("load", function load(aEvent) {
       if (aEvent.target.contentWindow.location == "about:blank")
         return;
-      content.gSubDialog._frame.removeEventListener("load", load);
+      content.gSubDialog._topDialog._frame.removeEventListener("load", load);
 
-      is(content.gSubDialog._frame.contentWindow.location.toString(), aURL,
+      is(content.gSubDialog._topDialog._frame.contentWindow.location.toString(), aURL,
          "Check the proper URL is loaded");
 
       // Check visibility
-      is_element_visible(content.gSubDialog._overlay, "Overlay is visible");
+      is_element_visible(content.gSubDialog._topDialog._overlay, "Overlay is visible");
 
       // Check that stylesheets were injected
-      let expectedStyleSheetURLs = content.gSubDialog._injectedStyleSheets.slice(0);
-      for (let styleSheet of content.gSubDialog._frame.contentDocument.styleSheets) {
+      let expectedStyleSheetURLs = content.gSubDialog._topDialog._injectedStyleSheets.slice(0);
+      for (let styleSheet of content.gSubDialog._topDialog._frame.contentDocument.styleSheets) {
         let i = expectedStyleSheetURLs.indexOf(styleSheet.href);
         if (i >= 0) {
           info("found " + styleSheet.href);
           expectedStyleSheetURLs.splice(i, 1);
         }
       }
       is(expectedStyleSheetURLs.length, 0, "All expectedStyleSheetURLs should have been found");
 
-      resolve(content.gSubDialog._frame.contentWindow);
+      resolve(content.gSubDialog._topDialog._frame.contentWindow);
     });
   });
 }
 
 /**
  * Waits a specified number of miliseconds for a specified event to be
  * fired on a specified element.
  *
@@ -188,28 +187,31 @@ function addPersistentStoragePerm(origin
 
 function promiseSiteDataManagerSitesUpdated() {
   return TestUtils.topicObserved("sitedatamanager:sites-updated", () => true);
 }
 
 function openSiteDataSettingsDialog() {
   let doc = gBrowser.selectedBrowser.contentDocument;
   let settingsBtn = doc.getElementById("siteDataSettings");
-  let dialogOverlay = doc.getElementById("dialogOverlay");
-  let dialogLoadPromise = promiseLoadSubDialog("chrome://browser/content/preferences/siteDataSettings.xul");
+  let dialogLoadPromise = openAndLoadSubDialog("chrome://browser/content/preferences/siteDataSettings.xul");
+  let dialog = content.gSubDialog._topDialog;
+  let dialogOverlay = dialog._overlay;
   let dialogInitPromise = TestUtils.topicObserved("sitedata-settings-init", () => true);
   let fullyLoadPromise = Promise.all([ dialogLoadPromise, dialogInitPromise ]).then(() => {
     is(dialogOverlay.style.visibility, "visible", "The Settings dialog should be visible");
   });
   settingsBtn.doCommand();
   return fullyLoadPromise;
 }
 
 function assertSitesListed(doc, origins) {
-  let frameDoc = doc.getElementById("dialogFrame").contentDocument;
+  let win = gBrowser.selectedBrowser.contentWindow;
+  let dialog = win.gSubDialog._topDialog;
+  let frameDoc = dialog._frame.contentDocument;
   let removeBtn = frameDoc.getElementById("removeSelected");
   let removeAllBtn = frameDoc.getElementById("removeAll");
   let sitesList = frameDoc.getElementById("sitesList");
   let totalSitesNumber = sitesList.getElementsByTagName("richlistitem").length;
   is(totalSitesNumber, origins.length, "Should list the right sites number");
   origins.forEach(origin => {
     let site = sitesList.querySelector(`richlistitem[data-origin="${origin}"]`);
     let host = site.getAttribute("host");