--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -1608,18 +1608,16 @@ pref("dom.ipc.reportProcessHangs", true)
 
 // Don't limit how many nodes we care about on desktop:
 pref("reader.parse-node-limit", 0);
 
 // On desktop, we want the URLs to be included here for ease of debugging,
 // and because (normally) these errors are not persisted anywhere.
 pref("reader.errors.includeURLs", true);
 
-pref("view_source.tab", true);
-
 pref("dom.serviceWorkers.enabled", true);
 
 // Enable Push API.
 pref("dom.push.enabled", true);
 
 // These are the thumbnail width/height set in about:newtab.
 // If you change this, ENSURE IT IS THE SAME SIZE SET
 // by about:newtab. These values are in CSS pixels.

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -2571,68 +2571,63 @@ function BrowserViewSourceOfDocument(aAr
                                  .outerWindowID;
     let URL = browser.currentURI.spec;
     args = { browser, outerWindowID, URL };
   } else {
     args = aArgsOrDocument;
   }
 
   let viewInternal = () => {
-    let inTab = Services.prefs.getBoolPref("view_source.tab");
-    if (inTab) {
-      let tabBrowser = gBrowser;
-      let preferredRemoteType;
-      if (args.browser) {
-        preferredRemoteType = args.browser.remoteType;
-      } else {
-        if (!tabBrowser) {
-          throw new Error("BrowserViewSourceOfDocument should be passed the " +
-                          "subject browser if called from a window without " +
-                          "gBrowser defined.");
-        }
-        // Some internal URLs (such as specific chrome: and about: URLs that are
-        // not yet remote ready) cannot be loaded in a remote browser.  View
-        // source in tab expects the new view source browser's remoteness to match
-        // that of the original URL, so disable remoteness if necessary for this
-        // URL.
-        preferredRemoteType =
-          E10SUtils.getRemoteTypeForURI(args.URL, gMultiProcessBrowser);
-      }
-
-      // In the case of popups, we need to find a non-popup browser window.
-      if (!tabBrowser || !window.toolbar.visible) {
-        // This returns only non-popup browser windows by default.
-        let browserWindow = RecentWindow.getMostRecentBrowserWindow();
-        tabBrowser = browserWindow.gBrowser;
-      }
-
-      // `viewSourceInBrowser` will load the source content from the page
-      // descriptor for the tab (when possible) or fallback to the network if
-      // that fails.  Either way, the view source module will manage the tab's
-      // location, so use "about:blank" here to avoid unnecessary redundant
-      // requests.
-      let tab = tabBrowser.loadOneTab("about:blank", {
-        relatedToCurrent: true,
-        inBackground: false,
-        preferredRemoteType,
-        sameProcessAsFrameLoader: args.browser ? args.browser.frameLoader : null,
-        triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
-      });
-      args.viewSourceBrowser = tabBrowser.getBrowserForTab(tab);
-      top.gViewSourceUtils.viewSourceInBrowser(args);
+    let tabBrowser = gBrowser;
+    let preferredRemoteType;
+    if (args.browser) {
+      preferredRemoteType = args.browser.remoteType;
     } else {
-      top.gViewSourceUtils.viewSource(args);
-    }
+      if (!tabBrowser) {
+        throw new Error("BrowserViewSourceOfDocument should be passed the " +
+                        "subject browser if called from a window without " +
+                        "gBrowser defined.");
+      }
+      // Some internal URLs (such as specific chrome: and about: URLs that are
+      // not yet remote ready) cannot be loaded in a remote browser.  View
+      // source in tab expects the new view source browser's remoteness to match
+      // that of the original URL, so disable remoteness if necessary for this
+      // URL.
+      preferredRemoteType =
+        E10SUtils.getRemoteTypeForURI(args.URL, gMultiProcessBrowser);
+    }
+
+    // In the case of popups, we need to find a non-popup browser window.
+    if (!tabBrowser || !window.toolbar.visible) {
+      // This returns only non-popup browser windows by default.
+      let browserWindow = RecentWindow.getMostRecentBrowserWindow();
+      tabBrowser = browserWindow.gBrowser;
+    }
+
+    // `viewSourceInBrowser` will load the source content from the page
+    // descriptor for the tab (when possible) or fallback to the network if
+    // that fails.  Either way, the view source module will manage the tab's
+    // location, so use "about:blank" here to avoid unnecessary redundant
+    // requests.
+    let tab = tabBrowser.loadOneTab("about:blank", {
+      relatedToCurrent: true,
+      inBackground: false,
+      preferredRemoteType,
+      sameProcessAsFrameLoader: args.browser ? args.browser.frameLoader : null,
+      triggeringPrincipal: Services.scriptSecurityManager.getSystemPrincipal(),
+    });
+    args.viewSourceBrowser = tabBrowser.getBrowserForTab(tab);
+    top.gViewSourceUtils.viewSourceInBrowser(args);
   };
 
   // Check if external view source is enabled.  If so, try it.  If it fails,
   // fallback to internal view source.
   if (Services.prefs.getBoolPref("view_source.editor.external")) {
     top.gViewSourceUtils
-       .openInExternalEditor(args, null, null, null, result => {
+       .openInExternalEditor(args, result => {
       if (!result) {
         viewInternal();
       }
     });
   } else {
     // Display using internal view source
     viewInternal();
   }
@@ -4482,18 +4477,17 @@ var XULBrowserWindow = {
         // Get the URI either from a channel or a pseudo-object
         if (aRequest instanceof nsIChannel || "URI" in aRequest) {
           location = aRequest.URI;
 
           // For keyword URIs clear the user typed value since they will be changed into real URIs
           if (location.scheme == "keyword" && aWebProgress.isTopLevel)
             gBrowser.userTypedValue = null;
 
-          canViewSource = !Services.prefs.getBoolPref("view_source.tab") ||
-                          location.scheme != "view-source";
+          canViewSource = location.scheme != "view-source";
 
           if (location.spec != "about:blank") {
             switch (aStatus) {
               case Components.results.NS_ERROR_NET_TIMEOUT:
                 msg = gNavigatorBundle.getString("nv_timeout");
                 break;
             }
           }

--- a/browser/base/content/nsContextMenu.js
+++ b/browser/base/content/nsContextMenu.js
@@ -861,19 +861,18 @@ nsContextMenu.prototype = {
   },
 
   reload(event) {
     BrowserReloadOrDuplicate(event);
   },
 
   // View Partial Source
   viewPartialSource(aContext) {
-    let inWindow = !Services.prefs.getBoolPref("view_source.tab");
     let {browser} = this;
-    let openSelectionFn = inWindow ? null : function() {
+    let openSelectionFn = function() {
       let tabBrowser = gBrowser;
       // In the case of popups, we need to find a non-popup browser window.
       // We might also not have a tabBrowser reference (if this isn't in a
       // a tabbrowser scope) or might have a fake/stub tabbrowser reference
       // (in the sidebar). Deal with those cases:
       if (!tabBrowser || !tabBrowser.loadOneTab || !window.toolbar.visible) {
         // This returns only non-popup browser windows by default.
         let browserWindow = RecentWindow.getMostRecentBrowserWindow();

--- a/browser/base/content/test/general/browser_viewSourceInTabOnViewSource.js
+++ b/browser/base/content/test/general/browser_viewSourceInTabOnViewSource.js
@@ -17,22 +17,16 @@ function wait_while_tab_is_busy() {
 var with_new_tab_opened = async function(options, taskFn) {
   let busyPromise = wait_while_tab_is_busy();
   let tab = await BrowserTestUtils.openNewForegroundTab(options.gBrowser, options.url, false);
   await busyPromise;
   await taskFn(tab.linkedBrowser);
   gBrowser.removeTab(tab);
 };
 
-add_task(async function() {
-  await SpecialPowers.pushPrefEnv({"set": [
-                                    ["view_source.tab", true],
-                                  ]});
-});
-
 add_task(async function test_regular_page() {
   function test_expect_view_source_enabled(browser) {
     ok(!XULBrowserWindow.canViewSource.hasAttribute("disabled"),
        "View Source should be enabled");
   }
 
   await with_new_tab_opened({
     gBrowser,

deleted file mode 100644
--- a/browser/base/content/viewSourceOverlay.xul
+++ /dev/null
@@ -1,26 +0,0 @@
-<?xml version="1.0"?>
-# 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/.
-
-<?xul-overlay href="chrome://browser/content/baseMenuOverlay.xul"?>
-
-<overlay id="viewSourceOverlay"
-         xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
-         xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
-
-<window id="viewSource">
-  <commandset id="baseMenuCommandSet"/>
-  <keyset id="baseMenuKeyset"/>
-  <stringbundleset id="stringbundleset"/>
-</window>
-
-<menubar id="viewSource-main-menubar">
-#ifdef XP_MACOSX
-  <menu id="windowMenu"/>
-  <menupopup id="menu_ToolsPopup"/>
-#endif
-  <menu id="helpMenu"/>
-</menubar>
-
-</overlay>

--- a/browser/base/jar.mn
+++ b/browser/base/jar.mn
@@ -1,15 +1,13 @@
 # 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/.
 browser.jar:
 %  content browser %content/browser/ contentaccessible=yes
-%  overlay chrome://global/content/viewSource.xul chrome://browser/content/viewSourceOverlay.xul
-%  overlay chrome://global/content/viewPartialSource.xul chrome://browser/content/viewSourceOverlay.xul
 
         content/browser/aboutDialog-appUpdater.js     (content/aboutDialog-appUpdater.js)
 *       content/browser/aboutDialog.xul               (content/aboutDialog.xul)
         content/browser/aboutDialog.js                (content/aboutDialog.js)
         content/browser/aboutDialog.css               (content/aboutDialog.css)
         content/browser/aboutRobots.xhtml             (content/aboutRobots.xhtml)
         content/browser/aboutRobots.js                (content/aboutRobots.js)
         content/browser/aboutRobots.css               (content/aboutRobots.css)
@@ -129,17 +127,16 @@ browser.jar:
 *       content/browser/webext-panels.xul             (content/webext-panels.xul)
 *       content/browser/baseMenuOverlay.xul           (content/baseMenuOverlay.xul)
         content/browser/nsContextMenu.js              (content/nsContextMenu.js)
 # XXX: We should exclude this one as well (bug 71895)
 *       content/browser/hiddenWindow.xul              (content/hiddenWindow.xul)
 #ifdef XP_MACOSX
 *       content/browser/macBrowserOverlay.xul         (content/macBrowserOverlay.xul)
 #endif
-*       content/browser/viewSourceOverlay.xul         (content/viewSourceOverlay.xul)
 #ifndef XP_MACOSX
 *       content/browser/webrtcIndicator.xul           (content/webrtcIndicator.xul)
         content/browser/webrtcIndicator.js            (content/webrtcIndicator.js)
 #endif
 # the following files are browser-specific overrides
 *       content/browser/license.html                  (/toolkit/content/license.html)
 % override chrome://global/content/license.html chrome://browser/content/license.html
         content/browser/blockedSite.xhtml               (content/blockedSite.xhtml)

--- a/devtools/client/shared/view-source.js
+++ b/devtools/client/shared/view-source.js
@@ -165,21 +165,14 @@ exports.viewSourceInScratchpad = Task.as
  *
  * @param {Toolbox} toolbox
  * @param {string} sourceURL
  * @param {number} sourceLine
  *
  * @return {Promise}
  */
 exports.viewSource = Task.async(function* (toolbox, sourceURL, sourceLine) {
-  // Attempt to access view source via a browser first, which may display it in
-  // a tab, if enabled.
-  let browserWin = Services.wm.getMostRecentWindow(gDevTools.chromeWindowType);
-  if (browserWin && browserWin.BrowserViewSourceOfDocument) {
-    return browserWin.BrowserViewSourceOfDocument({
-      URL: sourceURL,
-      lineNumber: sourceLine
-    });
-  }
   let utils = toolbox.gViewSourceUtils;
-  utils.viewSource(sourceURL, null, toolbox.doc, sourceLine || 0);
-  return null;
+  utils.viewSource({
+    URL: sourceURL,
+    lineNumber: sourceLine || 0,
+  });
 });

--- a/devtools/client/webconsole/hudservice.js
+++ b/devtools/client/webconsole/hudservice.js
@@ -392,27 +392,17 @@ WebConsole.prototype = {
    * Open a link in Firefox's view source.
    *
    * @param string sourceURL
    *        The URL of the file.
    * @param integer sourceLine
    *        The line number which should be highlighted.
    */
   viewSource(sourceURL, sourceLine) {
-    // Attempt to access view source via a browser first, which may display it in
-    // a tab, if enabled.
-    let browserWin = Services.wm.getMostRecentWindow(gDevTools.chromeWindowType);
-    if (browserWin && browserWin.BrowserViewSourceOfDocument) {
-      return browserWin.BrowserViewSourceOfDocument({
-        URL: sourceURL,
-        lineNumber: sourceLine
-      });
-    }
-    return this.gViewSourceUtils.viewSource(
-      sourceURL, null, this.iframeWindow.document, sourceLine || 0);
+    this.gViewSourceUtils.viewSource({ URL: sourceURL, lineNumber: sourceLine || 0 });
   },
 
   /**
    * Tries to open a Stylesheet file related to the web page for the web console
    * instance in the Style Editor. If the file is not found, it is opened in
    * source view instead.
    *
    * Manually handle the case where toolbox does not exist (Browser Console).

--- a/toolkit/components/viewsource/ViewSourceBrowser.jsm
+++ b/toolkit/components/viewsource/ViewSourceBrowser.jsm
@@ -21,20 +21,16 @@ this.EXPORTED_SYMBOLS = ["ViewSourceBrow
 // needed into any new ones.
 var gKnownBrowsers = new WeakSet();
 
 /**
  * ViewSourceBrowser manages the view source <browser> from the chrome side.
  * It's companion frame script, viewSource-content.js, needs to be loaded as a
  * frame script into the browser being managed.
  *
- * For a view source window using viewSource.xul, the script viewSource.js in
- * the window extends an instance of this with more window specific functions.
- * The page script takes care of loading the companion frame script.
- *
  * For a view source tab (or some other non-window case), an instance of this is
  * created by viewSourceUtils.js to wrap the <browser>.  The frame script will
  * be loaded by this module at construction time.
  */
 this.ViewSourceBrowser = function ViewSourceBrowser(aBrowser) {
   this._browser = aBrowser;
   this.init();
 };
@@ -72,23 +68,18 @@ ViewSourceBrowser.prototype = {
    * This should be called as soon as the script loads. When this function
    * executes, we can assume the DOM content has not yet loaded.
    */
   init() {
     this.messages.forEach((msgName) => {
       this.mm.addMessageListener(msgName, this);
     });
 
-    // If we have a known <browser> already, load the frame script here.  This
-    // is not true for the window case, as the element does not exist until the
-    // XUL document loads.  For that case, the frame script is loaded by
-    // viewSource.js.
-    if (this._browser) {
-      this.loadFrameScript();
-    }
+    // If we have a known <browser> already, load the frame script here.
+    this.loadFrameScript();
   },
 
   /**
    * This should be called when the window is closing. This function should
    * clean up event and message listeners.
    */
   uninit() {
     this.messages.forEach((msgName) => {
@@ -155,17 +146,16 @@ ViewSourceBrowser.prototype = {
     }
     return this._bundle = Services.strings.createBundle(BUNDLE_URL);
   },
 
   /**
    * Loads the source for a URL while applying some optional features if
    * enabled.
    *
-   * For the viewSource.xul window, this is called by onXULLoaded above.
    * For view source in a specific browser, this is manually called after
    * this object is constructed.
    *
    * This takes a single object argument containing:
    *
    *   URL (required):
    *     A string URL for the page we'd like to view the source of.
    *   browser:

deleted file mode 100644
--- a/toolkit/components/viewsource/content/viewPartialSource.js
+++ /dev/null
@@ -1,24 +0,0 @@
-// -*- 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/. */
-
-/* import-globals-from viewSource.js */
-
-ChromeUtils.import("resource://gre/modules/Services.jsm");
-
-function onLoadViewPartialSource() {
-  // check the view_source.wrap_long_lines pref
-  // and set the menuitem's checked attribute accordingly
-  let wrapLongLines = Services.prefs.getBoolPref("view_source.wrap_long_lines");
-  document.getElementById("menu_wrapLongLines")
-          .setAttribute("checked", wrapLongLines);
-  document.getElementById("menu_highlightSyntax")
-          .setAttribute("checked",
-                        Services.prefs.getBoolPref("view_source.syntax_highlight"));
-
-  let args = window.arguments[0];
-  viewSourceChrome.loadViewSourceFromSelection(args.URI, args.drawSelection, args.baseURI);
-  window.content.focus();
-}

deleted file mode 100644
--- a/toolkit/components/viewsource/content/viewPartialSource.xul
+++ /dev/null
@@ -1,163 +0,0 @@
-<?xml version="1.0"?>
-# -*- Mode: HTML -*-
-# 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/.
-
-<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
-<?xml-stylesheet href="chrome://global/content/viewSource.css" type="text/css"?>
-<?xml-stylesheet href="chrome://mozapps/skin/viewsource/viewsource.css" type="text/css"?>
-<?xul-overlay href="chrome://global/content/editMenuOverlay.xul"?>
-
-<!DOCTYPE window [
-<!ENTITY % brandDTD SYSTEM "chrome://branding/locale/brand.dtd" >
-%brandDTD;
-<!ENTITY % sourceDTD SYSTEM "chrome://global/locale/viewSource.dtd" >
-%sourceDTD;
-]>
-
-<window id="viewSource"
-        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-        onload="onLoadViewPartialSource();"
-        contenttitlesetting="true"
-        title="&mainWindow.title;"
-        titlemodifier="&mainWindow.titlemodifier;"
-        titlepreface=""
-        titlemenuseparator ="&mainWindow.titlemodifierseparator;"
-        windowtype="navigator:view-source"
-        width="500" height="300"
-        screenX="10" screenY="10"
-        persist="screenX screenY width height sizemode">
-
-  <script type="application/javascript" src="chrome://global/content/globalOverlay.js"/>
-  <script type="application/javascript" src="chrome://global/content/printUtils.js"/>
-  <script type="application/javascript" src="chrome://global/content/viewSource.js"/>
-  <script type="application/javascript" src="chrome://global/content/viewPartialSource.js"/>
-  <script type="application/javascript" src="chrome://global/content/viewZoomOverlay.js"/>
-  <script type="application/javascript" src="chrome://global/content/contentAreaUtils.js"/>
-
-  <stringbundle id="viewSourceBundle" src="chrome://global/locale/viewSource.properties"/>
-
-  <command id="cmd_savePage" oncommand="ViewSourceSavePage();"/>
-  <command id="cmd_print" oncommand="PrintUtils.printWindow(gBrowser.outerWindowID, gBrowser);"/>
-  <command id="cmd_printpreview" oncommand="PrintUtils.printPreview(PrintPreviewListener);"/>
-  <command id="cmd_pagesetup" oncommand="PrintUtils.showPageSetup();"/>
-  <command id="cmd_close" oncommand="window.close();"/>
-  <commandset id="editMenuCommands"/>
-  <command id="cmd_find"
-           oncommand="document.getElementById('FindToolbar').onFindCommand();"/>
-  <command id="cmd_findAgain"
-           oncommand="document.getElementById('FindToolbar').onFindAgainCommand(false);"/>
-  <command id="cmd_findPrevious"
-           oncommand="document.getElementById('FindToolbar').onFindAgainCommand(true);"/>
-  <command id="cmd_goToLine" oncommand="viewSourceChrome.promptAndGoToLine();" disabled="true"/>
-  <command id="cmd_highlightSyntax" oncommand="viewSourceChrome.toggleSyntaxHighlighting();"/>
-  <command id="cmd_wrapLongLines" oncommand="viewSourceChrome.toggleWrapping();"/>
-  <command id="cmd_textZoomReduce" oncommand="ZoomManager.reduce();"/>
-  <command id="cmd_textZoomEnlarge" oncommand="ZoomManager.enlarge();"/>
-  <command id="cmd_textZoomReset" oncommand="ZoomManager.reset();"/>
-
-  <keyset id="editMenuKeys"/>
-  <keyset id="viewSourceKeys">
-    <key id="key_savePage" key="&savePageCmd.commandkey;" modifiers="accel" command="cmd_savePage"/>
-    <key id="key_print" key="&printCmd.commandkey;" modifiers="accel" command="cmd_print"/>
-    <key id="key_close" key="&closeCmd.commandkey;" modifiers="accel" command="cmd_close"/>
-    <key keycode="VK_ESCAPE" command="cmd_close"/>
-
-    <key id="key_textZoomEnlarge" key="&textEnlarge.commandkey;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomEnlarge2" key="&textEnlarge.commandkey2;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomEnlarge3" key="&textEnlarge.commandkey3;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomReduce"  key="&textReduce.commandkey;" command="cmd_textZoomReduce" modifiers="accel"/>
-    <key id="key_textZoomReduce2"  key="&textReduce.commandkey2;" command="cmd_textZoomReduce" modifiers="accel"/>
-    <key id="key_textZoomReset" key="&textReset.commandkey;" command="cmd_textZoomReset" modifiers="accel"/>
-    <key id="key_textZoomReset2" key="&textReset.commandkey2;" command="cmd_textZoomReset" modifiers="accel"/>
-  </keyset>
-
-  <menupopup id="viewSourceContextMenu">
-    <menuitem id="cMenu_findAgain"/>
-    <menuseparator/>
-    <menuitem id="cMenu_copy"/>
-    <menuitem id="context-copyLink"
-              label="&copyLinkCmd.label;"
-              accesskey="&copyLinkCmd.accesskey;"
-              oncommand="viewSourceChrome.onContextMenuCopyLinkOrEmail();"/>
-    <menuitem id="context-copyEmail"
-              label="&copyEmailCmd.label;"
-              accesskey="&copyEmailCmd.accesskey;"
-              oncommand="viewSourceChrome.onContextMenuCopyLinkOrEmail();"/>
-    <menuseparator/>
-    <menuitem id="cMenu_selectAll"/>
-  </menupopup>
-
-  <!-- Menu -->
-  <toolbox id="viewSource-toolbox">
-    <menubar id="viewSource-main-menubar">
-
-      <menu id="menu_file" label="&fileMenu.label;" accesskey="&fileMenu.accesskey;">
-        <menupopup id="menu_FilePopup">
-          <menuitem key="key_savePage" command="cmd_savePage" id="menu_savePage"
-                    label="&savePageCmd.label;" accesskey="&savePageCmd.accesskey;"/>
-          <menuitem command="cmd_pagesetup" id="menu_pageSetup"
-                    label="&pageSetupCmd.label;" accesskey="&pageSetupCmd.accesskey;"/>
-#ifndef XP_MACOSX
-          <menuitem command="cmd_printpreview" id="menu_printPreview"
-                    label="&printPreviewCmd.label;" accesskey="&printPreviewCmd.accesskey;"/>
-#endif
-          <menuitem key="key_print" command="cmd_print" id="menu_print"
-                    label="&printCmd.label;" accesskey="&printCmd.accesskey;"/>
-          <menuseparator/>
-          <menuitem key="key_close" command="cmd_close" id="menu_close"
-                    label="&closeCmd.label;" accesskey="&closeCmd.accesskey;"/>
-        </menupopup>
-      </menu>
-
-      <menu id="menu_edit">
-        <menupopup id="editmenu-popup">
-          <menuitem id="menu_undo"/>
-          <menuitem id="menu_redo"/>
-          <menuseparator/>
-          <menuitem id="menu_cut"/>
-          <menuitem id="menu_copy"/>
-          <menuitem id="menu_paste"/>
-          <menuitem id="menu_delete"/>
-          <menuseparator/>
-          <menuitem id="menu_selectAll"/>
-          <menuseparator/>
-          <menuitem id="menu_find"/>
-          <menuitem id="menu_findAgain"/>
-        </menupopup>
-      </menu>
-
-      <menu id="menu_view" label="&viewMenu.label;" accesskey="&viewMenu.accesskey;">
-        <menupopup id="viewmenu-popup">
-          <menu id="viewTextZoomMenu" label="&menu_textSize.label;" accesskey="&menu_textSize.accesskey;">
-            <menupopup>
-              <menuitem id="menu_textEnlarge" command="cmd_textZoomEnlarge"
-                        label="&menu_textEnlarge.label;" accesskey="&menu_textEnlarge.accesskey;"
-                        key="key_textZoomEnlarge"/>
-              <menuitem id="menu_textReduce" command="cmd_textZoomReduce"
-                        label="&menu_textReduce.label;" accesskey="&menu_textReduce.accesskey;"
-                        key="key_textZoomReduce"/>
-              <menuseparator/>
-              <menuitem id="menu_textReset" command="cmd_textZoomReset"
-                        label="&menu_textReset.label;" accesskey="&menu_textReset.accesskey;"
-                        key="key_textZoomReset"/>
-            </menupopup>
-          </menu>
-          <menuseparator/>
-          <menuitem id="menu_wrapLongLines" type="checkbox" command="cmd_wrapLongLines"
-                    label="&menu_wrapLongLines.title;" accesskey="&menu_wrapLongLines.accesskey;"/>
-          <menuitem type="checkbox" id="menu_highlightSyntax" command="cmd_highlightSyntax"
-                    label="&menu_highlightSyntax.label;" accesskey="&menu_highlightSyntax.accesskey;"/>
-        </menupopup>
-      </menu>
-    </menubar>
-  </toolbox>
-
-  <vbox id="appcontent" flex="1">
-    <browser id="content" type="content" primary="true" name="content" src="about:blank" flex="1"
-             disablehistory="true" context="viewSourceContextMenu" />
-    <findbar id="FindToolbar" browserid="content"/>
-  </vbox>
-
-</window>

deleted file mode 100644
--- a/toolkit/components/viewsource/content/viewSource.css
+++ /dev/null
@@ -1,7 +0,0 @@
-/* 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/. */
-
-toolbar[printpreview="true"] {
-  -moz-binding: url("chrome://global/content/printPreviewBindings.xml#printpreviewtoolbar");
-}

deleted file mode 100644
--- a/toolkit/components/viewsource/content/viewSource.js
+++ /dev/null
@@ -1,866 +0,0 @@
-// -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
-
-/* import-globals-from ../../../content/globalOverlay.js */
-/* import-globals-from ../../printing/content/printUtils.js */
-/* import-globals-from ../../../content/viewZoomOverlay.js */
-/* import-globals-from ../../../content/contentAreaUtils.js */
-
-/* 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/. */
-
-ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
-ChromeUtils.import("resource://gre/modules/ViewSourceBrowser.jsm");
-
-ChromeUtils.defineModuleGetter(this, "Services",
-  "resource://gre/modules/Services.jsm");
-ChromeUtils.defineModuleGetter(this, "CharsetMenu",
-  "resource://gre/modules/CharsetMenu.jsm");
-ChromeUtils.defineModuleGetter(this, "Deprecated",
-  "resource://gre/modules/Deprecated.jsm");
-
-/* global gBrowser, gViewSourceBundle, gContextMenu */
-[
-  ["gBrowser",          "content"],
-  ["gViewSourceBundle", "viewSourceBundle"],
-  ["gContextMenu",      "viewSourceContextMenu"]
-].forEach(function([name, id]) {
-  Object.defineProperty(window, name, {
-    configurable: true,
-    enumerable: true,
-    get() {
-      var element = document.getElementById(id);
-      if (!element)
-        return null;
-      delete window[name];
-      return window[name] = element;
-    },
-  });
-});
-
-/**
- * ViewSourceChrome is the primary interface for interacting with
- * the view source browser from a self-contained window.  It extends
- * ViewSourceBrowser with additional things needed inside the special window.
- *
- * It initializes itself on script load.
- */
-function ViewSourceChrome() {
-  ViewSourceBrowser.call(this);
-}
-
-ViewSourceChrome.prototype = {
-  __proto__: ViewSourceBrowser.prototype,
-
-  /**
-   * The <browser> that will be displaying the view source content.
-   */
-  get browser() {
-    return gBrowser;
-  },
-
-  /**
-   * The context menu, when opened from the content process, sends
-   * up a chunk of serialized data describing the items that the
-   * context menu is being opened on. This allows us to avoid using
-   * CPOWs.
-   */
-  contextMenuData: {},
-
-  /**
-   * These are the messages that ViewSourceChrome will listen for
-   * from the frame script it injects. Any message names added here
-   * will automatically have ViewSourceChrome listen for those messages,
-   * and remove the listeners on teardown.
-   */
-  messages: ViewSourceBrowser.prototype.messages.concat([
-    "ViewSource:SourceLoaded",
-    "ViewSource:SourceUnloaded",
-    "ViewSource:Close",
-    "ViewSource:OpenURL",
-    "ViewSource:ContextMenuOpening",
-  ]),
-
-  /**
-   * This called via ViewSourceBrowser's constructor.  This should be called as
-   * soon as the script loads.  When this function executes, we can assume the
-   * DOM content has not yet loaded.
-   */
-  init() {
-    this.mm.loadFrameScript("chrome://global/content/viewSource-content.js", true);
-
-    this.shouldWrap = Services.prefs.getBoolPref("view_source.wrap_long_lines");
-    this.shouldHighlight =
-      Services.prefs.getBoolPref("view_source.syntax_highlight");
-
-    addEventListener("load", this);
-    addEventListener("unload", this);
-    addEventListener("AppCommand", this, true);
-    addEventListener("MozSwipeGesture", this, true);
-
-    ViewSourceBrowser.prototype.init.call(this);
-  },
-
-  /**
-   * This should be called when the window is closing. This function should
-   * clean up event and message listeners.
-   */
-  uninit() {
-    ViewSourceBrowser.prototype.uninit.call(this);
-
-    // "load" event listener is removed in its handler, to
-    // ensure we only fire it once.
-    removeEventListener("unload", this);
-    removeEventListener("AppCommand", this, true);
-    removeEventListener("MozSwipeGesture", this, true);
-    gContextMenu.removeEventListener("popupshowing", this);
-    gContextMenu.removeEventListener("popuphidden", this);
-    Services.els.removeSystemEventListener(this.browser, "dragover", this,
-                                           true);
-    Services.els.removeSystemEventListener(this.browser, "drop", this, true);
-  },
-
-  /**
-   * Anything added to the messages array will get handled here, and should
-   * get dispatched to a specific function for the message name.
-   */
-  receiveMessage(message) {
-    let data = message.data;
-
-    switch (message.name) {
-      // Begin messages from super class
-      case "ViewSource:PromptAndGoToLine":
-        this.promptAndGoToLine();
-        break;
-      case "ViewSource:GoToLine:Success":
-        this.onGoToLineSuccess(data.lineNumber);
-        break;
-      case "ViewSource:GoToLine:Failed":
-        this.onGoToLineFailed();
-        break;
-      case "ViewSource:StoreWrapping":
-        this.storeWrapping(data.state);
-        break;
-      case "ViewSource:StoreSyntaxHighlighting":
-        this.storeSyntaxHighlighting(data.state);
-        break;
-      // End messages from super class
-      case "ViewSource:SourceLoaded":
-        this.onSourceLoaded();
-        break;
-      case "ViewSource:SourceUnloaded":
-        this.onSourceUnloaded();
-        break;
-      case "ViewSource:Close":
-        this.close();
-        break;
-      case "ViewSource:OpenURL":
-        this.openURL(data.URL);
-        break;
-      case "ViewSource:ContextMenuOpening":
-        this.onContextMenuOpening(data.isLink, data.isEmail, data.href);
-        if (this.browser.isRemoteBrowser) {
-          this.openContextMenu(data.screenX, data.screenY);
-        }
-        break;
-    }
-  },
-
-  /**
-   * Any events should get handled here, and should get dispatched to
-   * a specific function for the event type.
-   */
-  handleEvent(event) {
-    switch (event.type) {
-      case "unload":
-        this.uninit();
-        break;
-      case "load":
-        this.onXULLoaded();
-        break;
-      case "AppCommand":
-        this.onAppCommand(event);
-        break;
-      case "MozSwipeGesture":
-        this.onSwipeGesture(event);
-        break;
-      case "popupshowing":
-        this.onContextMenuShowing(event);
-        break;
-      case "popuphidden":
-        this.onContextMenuHidden(event);
-        break;
-      case "dragover":
-        this.onDragOver(event);
-        break;
-      case "drop":
-        this.onDrop(event);
-        break;
-    }
-  },
-
-  /**
-   * Getter that returns whether or not the view source browser
-   * has history enabled on it.
-   */
-  get historyEnabled() {
-    return !this.browser.hasAttribute("disablehistory");
-  },
-
-  /**
-   * Getter for the message manager used to communicate with the view source
-   * browser.
-   *
-   * In this window version of view source, we use the window message manager
-   * for loading scripts and listening for messages so that if we switch
-   * remoteness of the browser (which we might do if we're attempting to load
-   * the document source out of the network cache), we automatically re-load
-   * the frame script.
-   */
-  get mm() {
-    return window.messageManager;
-  },
-
-  /**
-   * Getter for the nsIWebNavigation of the view source browser.
-   */
-  get webNav() {
-    return this.browser.webNavigation;
-  },
-
-  /**
-   * Send the browser forward in its history.
-   */
-  goForward() {
-    this.browser.goForward();
-  },
-
-  /**
-   * Send the browser backward in its history.
-   */
-  goBack() {
-    this.browser.goBack();
-  },
-
-  /**
-   * This should be called once when the DOM has finished loading. Here we
-   * set the state of various menu items, and add event listeners to
-   * DOM nodes.
-   *
-   * This is also the place where we handle any arguments that have been
-   * passed to viewSource.xul.
-   *
-   * Modern consumers should pass a single object argument to viewSource.xul:
-   *
-   *   URL (required):
-   *     A string URL for the page we'd like to view the source of.
-   *   browser:
-   *     The browser containing the document that we would like to view the
-   *     source of. This argument is optional if outerWindowID is not passed.
-   *   outerWindowID (optional):
-   *     The outerWindowID of the content window containing the document that
-   *     we want to view the source of. This is the only way of attempting to
-   *     load the source out of the network cache.
-   *   lineNumber (optional):
-   *     The line number to focus on once the source is loaded.
-   *
-   * The deprecated API has the opener pass in a number of arguments:
-   *
-   * arg[0] - URL string.
-   * arg[1] - Charset value string in the form 'charset=xxx'.
-   * arg[2] - Page descriptor from nsIWebPageDescriptor used to load content
-   *          from the cache.
-   * arg[3] - Line number to go to.
-   * arg[4] - Boolean for whether charset was forced by the user
-   */
-  onXULLoaded() {
-    // This handler should only ever run the first time the XUL is loaded.
-    removeEventListener("load", this);
-
-    let wrapMenuItem = document.getElementById("menu_wrapLongLines");
-    if (this.shouldWrap) {
-      wrapMenuItem.setAttribute("checked", "true");
-    }
-
-    let highlightMenuItem = document.getElementById("menu_highlightSyntax");
-    if (this.shouldHighlight) {
-      highlightMenuItem.setAttribute("checked", "true");
-    }
-
-    gContextMenu.addEventListener("popupshowing", this);
-    gContextMenu.addEventListener("popuphidden", this);
-
-    Services.els.addSystemEventListener(this.browser, "dragover", this, true);
-    Services.els.addSystemEventListener(this.browser, "drop", this, true);
-
-    if (!this.historyEnabled) {
-      // Disable the BACK and FORWARD commands and hide the related menu items.
-      let viewSourceNavigation = document.getElementById("viewSourceNavigation");
-      if (viewSourceNavigation) {
-        viewSourceNavigation.setAttribute("disabled", "true");
-        viewSourceNavigation.setAttribute("hidden", "true");
-      }
-    }
-
-    // We require the first argument to do any loading of source.
-    // otherwise, we're done.
-    if (!window.arguments[0]) {
-      return undefined;
-    }
-
-    if (typeof window.arguments[0] == "string") {
-      // We're using the deprecated API
-      return this._loadViewSourceDeprecated(window.arguments);
-    }
-
-    // We're using the modern API, which allows us to view the
-    // source of documents from out of process browsers.
-    let args = window.arguments[0];
-
-    // viewPartialSource.js will take care of loading the content in partial mode.
-    if (!args.partial) {
-      this.loadViewSource(args);
-    }
-
-    return undefined;
-  },
-
-  /**
-   * This is the deprecated API for viewSource.xul, for old-timer consumers.
-   * This API might eventually go away.
-   */
-  _loadViewSourceDeprecated(aArguments) {
-    Deprecated.warning("The arguments you're passing to viewSource.xul " +
-                       "are using an out-of-date API.",
-                       "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-    // Parse the 'arguments' supplied with the dialog.
-    //    arg[0] - URL string.
-    //    arg[1] - Charset value in the form 'charset=xxx'.
-    //    arg[2] - Page descriptor used to load content from the cache.
-    //    arg[3] - Line number to go to.
-    //    arg[4] - Whether charset was forced by the user
-
-    if (aArguments[2]) {
-      let pageDescriptor = aArguments[2];
-      if (Cu.isCrossProcessWrapper(pageDescriptor)) {
-        throw new Error("Cannot pass a CPOW as the page descriptor to viewSource.xul.");
-      }
-    }
-
-    if (this.browser.isRemoteBrowser) {
-      throw new Error("Deprecated view source API should not use a remote browser.");
-    }
-
-    let forcedCharSet;
-    if (aArguments[4] && aArguments[1].startsWith("charset=")) {
-      forcedCharSet = aArguments[1].split("=")[1];
-    }
-
-    this.sendAsyncMessage("ViewSource:LoadSourceDeprecated", {
-      URL: aArguments[0],
-      lineNumber: aArguments[3],
-      forcedCharSet,
-    }, {
-      pageDescriptor: aArguments[2],
-    });
-  },
-
-  /**
-   * Handler for the AppCommand event.
-   *
-   * @param event
-   *        The AppCommand event being handled.
-   */
-  onAppCommand(event) {
-    event.stopPropagation();
-    switch (event.command) {
-      case "Back":
-        this.goBack();
-        break;
-      case "Forward":
-        this.goForward();
-        break;
-    }
-  },
-
-  /**
-   * Handler for the MozSwipeGesture event.
-   *
-   * @param event
-   *        The MozSwipeGesture event being handled.
-   */
-  onSwipeGesture(event) {
-    event.stopPropagation();
-    switch (event.direction) {
-      case SimpleGestureEvent.DIRECTION_LEFT:
-        this.goBack();
-        break;
-      case SimpleGestureEvent.DIRECTION_RIGHT:
-        this.goForward();
-        break;
-      case SimpleGestureEvent.DIRECTION_UP:
-        goDoCommand("cmd_scrollTop");
-        break;
-      case SimpleGestureEvent.DIRECTION_DOWN:
-        goDoCommand("cmd_scrollBottom");
-        break;
-    }
-  },
-
-  /**
-   * Called as soon as the frame script reports that some source
-   * code has been loaded in the browser.
-   */
-  onSourceLoaded() {
-    document.getElementById("cmd_goToLine").removeAttribute("disabled");
-
-    if (this.historyEnabled) {
-      this.updateCommands();
-    }
-
-    this.browser.focus();
-  },
-
-  /**
-   * Called as soon as the frame script reports that some source
-   * code has been unloaded from the browser.
-   */
-  onSourceUnloaded() {
-    // Disable "go to line" while reloading due to e.g. change of charset
-    // or toggling of syntax highlighting.
-    document.getElementById("cmd_goToLine").setAttribute("disabled", "true");
-  },
-
-  /**
-   * Called by clicks on a menu populated by CharsetMenu.jsm to
-   * change the selected character set.
-   *
-   * @param event
-   *        The click event on a character set menuitem.
-   */
-  onSetCharacterSet(event) {
-    if (event.target.hasAttribute("charset")) {
-      let charset = event.target.getAttribute("charset");
-
-      // If we don't have history enabled, we have to do a reload in order to
-      // show the character set change. See bug 136322.
-      this.sendAsyncMessage("ViewSource:SetCharacterSet", {
-        charset,
-        doPageLoad: this.historyEnabled,
-      });
-
-      if (!this.historyEnabled) {
-        this.browser
-            .reloadWithFlags(Ci.nsIWebNavigation.LOAD_FLAGS_CHARSET_CHANGE);
-      }
-    }
-  },
-
-  /**
-   * Called from the frame script when the context menu is about to
-   * open. This tells ViewSourceChrome things about the item that
-   * the context menu is being opened on. This should be called before
-   * the popupshowing event handler fires.
-   */
-  onContextMenuOpening(isLink, isEmail, href) {
-    this.contextMenuData = { isLink, isEmail, href, isOpen: true };
-  },
-
-  /**
-   * Event handler for the popupshowing event on the context menu.
-   * This handler is responsible for setting the state on various
-   * menu items in the context menu, and reads values that were sent
-   * up from the frame script and stashed into this.contextMenuData.
-   *
-   * @param event
-   *        The popupshowing event for the context menu.
-   */
-  onContextMenuShowing(event) {
-    let copyLinkMenuItem = document.getElementById("context-copyLink");
-    copyLinkMenuItem.hidden = !this.contextMenuData.isLink;
-
-    let copyEmailMenuItem = document.getElementById("context-copyEmail");
-    copyEmailMenuItem.hidden = !this.contextMenuData.isEmail;
-  },
-
-  /**
-   * Called when the user chooses the "Copy Link" or "Copy Email"
-   * menu items in the context menu. Copies the relevant selection
-   * into the system clipboard.
-   */
-  onContextMenuCopyLinkOrEmail() {
-    // It doesn't make any sense to call this if the context menu
-    // isn't open...
-    if (!this.contextMenuData.isOpen) {
-      return;
-    }
-
-    let clipboard = Cc["@mozilla.org/widget/clipboardhelper;1"]
-                      .getService(Ci.nsIClipboardHelper);
-    clipboard.copyString(this.contextMenuData.href);
-  },
-
-  /**
-   * Called when the context menu closes, and invalidates any data
-   * that the frame script might have sent up about what the context
-   * menu was opened on.
-   */
-  onContextMenuHidden(event) {
-    this.contextMenuData = {
-      isOpen: false,
-    };
-  },
-
-  /**
-   * Called when the user drags something over the content browser.
-   */
-  onDragOver(event) {
-    // For drags that appear to be internal text (for example, tab drags),
-    // set the dropEffect to 'none'. This prevents the drop even if some
-    // other listener cancelled the event.
-    let types = event.dataTransfer.types;
-    if (types.includes("text/x-moz-text-internal") && !types.includes("text/plain")) {
-        event.dataTransfer.dropEffect = "none";
-        event.stopPropagation();
-        event.preventDefault();
-    }
-
-    if (Services.droppedLinkHandler.canDropLink(event, false)) {
-      event.preventDefault();
-    }
-  },
-
-  /**
-   * Called twhen the user drops something onto the content browser.
-   */
-  onDrop(event) {
-    if (event.defaultPrevented)
-      return;
-
-    let name = { };
-    let uri;
-    try {
-      // Pass true to prevent the dropping of javascript:/data: URIs
-      uri = Services.droppedLinkHandler.dropLink(event, name, true);
-    } catch (e) {
-      return;
-    }
-
-    if (uri) {
-      this.loadURL(uri);
-    }
-  },
-
-  /**
-   * For remote browsers, the contextmenu event is received in the
-   * content process, and a message is sent up from the frame script
-   * to ViewSourceChrome, but then it stops. The event does not bubble
-   * up to the point that the popup is opened in the parent process.
-   * ViewSourceChrome is responsible for opening up the context menu in
-   * that case. This is called when we receive the contextmenu message
-   * from the child, and we know that the browser is currently remote.
-   *
-   * @param screenX
-   *        The screenX coordinate to open the popup at.
-   * @param screenY
-   *        The screenY coordinate to open the popup at.
-   */
-  openContextMenu(screenX, screenY) {
-    gContextMenu.openPopupAtScreen(screenX, screenY, true);
-  },
-
-  /**
-   * Loads the source of a URL. This will probably end up hitting the
-   * network.
-   *
-   * @param URL
-   *        A URL string to be opened in the view source browser.
-   */
-  loadURL(URL) {
-    this.sendAsyncMessage("ViewSource:LoadSource", { URL });
-  },
-
-  /**
-   * Updates any commands that are dependant on command broadcasters.
-   */
-  updateCommands() {
-    let backBroadcaster = document.getElementById("Browser:Back");
-    let forwardBroadcaster = document.getElementById("Browser:Forward");
-
-    if (this.webNav.canGoBack) {
-      backBroadcaster.removeAttribute("disabled");
-    } else {
-      backBroadcaster.setAttribute("disabled", "true");
-    }
-    if (this.webNav.canGoForward) {
-      forwardBroadcaster.removeAttribute("disabled");
-    } else {
-      forwardBroadcaster.setAttribute("disabled", "true");
-    }
-  },
-
-  /**
-   * Reloads the browser, bypassing the network cache.
-   */
-  reload() {
-    this.browser.reloadWithFlags(Ci.nsIWebNavigation.LOAD_FLAGS_BYPASS_PROXY |
-                                 Ci.nsIWebNavigation.LOAD_FLAGS_BYPASS_CACHE);
-  },
-
-  /**
-   * Closes the view source window.
-   */
-  close() {
-    window.close();
-  },
-
-  /**
-   * Called when the user clicks on the "Wrap Long Lines" menu item.
-   */
-  toggleWrapping() {
-    this.shouldWrap = !this.shouldWrap;
-    this.sendAsyncMessage("ViewSource:ToggleWrapping");
-  },
-
-  /**
-   * Called when the user clicks on the "Syntax Highlighting" menu item.
-   */
-  toggleSyntaxHighlighting() {
-    this.shouldHighlight = !this.shouldHighlight;
-    this.sendAsyncMessage("ViewSource:ToggleSyntaxHighlighting");
-  },
-
-  /**
-   * Updates the "remote" attribute of the view source browser. This
-   * will remove the browser from the DOM, and then re-add it in the
-   * same place it was taken from.
-   *
-   * @param shouldBeRemote
-   *        True if the browser should be made remote. If the browsers
-   *        remoteness already matches this value, this function does
-   *        nothing.
-   * @param remoteType
-   *        The type of remote browser process.
-   */
-  updateBrowserRemoteness(shouldBeRemote, remoteType) {
-    if (this.browser.isRemoteBrowser == shouldBeRemote &&
-        this.browser.remoteType == remoteType) {
-      return;
-    }
-
-    let parentNode = this.browser.parentNode;
-    let nextSibling = this.browser.nextSibling;
-
-    // Removing and re-adding the browser from and to the DOM strips its XBL
-    // properties. Save and restore sameProcessAsFrameLoader. Note that when we
-    // restore sameProcessAsFrameLoader, there won't yet be a binding or
-    // setter. This works in conjunction with the hack in <xul:browser>'s
-    // constructor to re-get the weak reference to it.
-    let sameProcessAsFrameLoader = this.browser.sameProcessAsFrameLoader;
-
-    this.browser.remove();
-    if (shouldBeRemote) {
-      this.browser.setAttribute("remote", "true");
-      this.browser.setAttribute("remoteType", remoteType);
-    } else {
-      this.browser.removeAttribute("remote");
-      this.browser.removeAttribute("remoteType");
-    }
-
-    this.browser.sameProcessAsFrameLoader = sameProcessAsFrameLoader;
-
-    // If nextSibling was null, this will put the browser at
-    // the end of the list.
-    parentNode.insertBefore(this.browser, nextSibling);
-
-    if (shouldBeRemote) {
-      // We're going to send a message down to the remote browser
-      // to load the source content - however, in order for the
-      // contentWindowAsCPOW and contentDocumentAsCPOW values on
-      // the remote browser to be set, we must set up the
-      // RemoteWebProgress, which is lazily loaded. We only need
-      // contentWindowAsCPOW for the printing support, and this
-      // should go away once bug 1146454 is fixed, since we can
-      // then just pass the outerWindowID of the this.browser to
-      // PrintUtils.
-      this.browser.webProgress;
-    }
-  },
-};
-
-var viewSourceChrome = new ViewSourceChrome();
-
-/**
- * PrintUtils uses this to make Print Preview work.
- */
-var PrintPreviewListener = {
-  _ppBrowser: null,
-
-  getPrintPreviewBrowser() {
-    if (!this._ppBrowser) {
-      this._ppBrowser = document.createElement("browser");
-      this._ppBrowser.setAttribute("flex", "1");
-      this._ppBrowser.setAttribute("type", "content");
-    }
-
-    if (gBrowser.isRemoteBrowser) {
-      this._ppBrowser.setAttribute("remote", "true");
-    } else {
-      this._ppBrowser.removeAttribute("remote");
-    }
-
-    let findBar = document.getElementById("FindToolbar");
-    document.getElementById("appcontent")
-            .insertBefore(this._ppBrowser, findBar);
-
-    return this._ppBrowser;
-  },
-
-  getSourceBrowser() {
-    return gBrowser;
-  },
-
-  getNavToolbox() {
-    return document.getElementById("appcontent");
-  },
-
-  onEnter() {
-    let toolbox = document.getElementById("viewSource-toolbox");
-    toolbox.hidden = true;
-    gBrowser.collapsed = true;
-  },
-
-  onExit() {
-    this._ppBrowser.remove();
-    gBrowser.collapsed = false;
-    document.getElementById("viewSource-toolbox").hidden = false;
-  },
-
-  activateBrowser(browser) {
-    browser.docShellIsActive = true;
-  },
-};
-
-// viewZoomOverlay.js uses this
-function getBrowser() {
-  return gBrowser;
-}
-
-Object.defineProperty(this, "gPageLoader", {
-  configurable: true,
-  enumerable: true,
-  get() {
-    var webnav = viewSourceChrome.webNav;
-    if (!webnav)
-      return null;
-    delete this.gPageLoader;
-    this.gPageLoader = (webnav instanceof Ci.nsIWebPageDescriptor) ? webnav
-                                                                   : null;
-    return this.gPageLoader;
-  },
-});
-
-// Strips the |view-source:| for internalSave()
-function ViewSourceSavePage() {
-  internalSave(gBrowser.currentURI.spec.replace(/^view-source:/i, ""),
-               null, null, null, null, null, "SaveLinkTitle",
-               null, null, gBrowser.contentDocumentAsCPOW, null,
-               gPageLoader);
-}
-
-// Below are old deprecated functions and variables left behind for
-// compatibility reasons. These will be removed soon via bug 1159293.
-
-Object.defineProperty(this, "gLastLineFound", {
-  configurable: true,
-  enumerable: true,
-  get() {
-    Deprecated.warning("gLastLineFound is deprecated - please use " +
-                       "viewSourceChrome.lastLineFound instead.",
-                       "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-    return viewSourceChrome.lastLineFound;
-  },
-});
-
-function onLoadViewSource() {
-  Deprecated.warning("onLoadViewSource() is deprecated - please use " +
-                     "viewSourceChrome.onXULLoaded() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.onXULLoaded();
-}
-
-function isHistoryEnabled() {
-  Deprecated.warning("isHistoryEnabled() is deprecated - please use " +
-                     "viewSourceChrome.historyEnabled instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  return viewSourceChrome.historyEnabled;
-}
-
-function ViewSourceClose() {
-  Deprecated.warning("ViewSourceClose() is deprecated - please use " +
-                     "viewSourceChrome.close() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.close();
-}
-
-function ViewSourceReload() {
-  Deprecated.warning("ViewSourceReload() is deprecated - please use " +
-                     "viewSourceChrome.reload() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.reload();
-}
-
-function getWebNavigation() {
-  Deprecated.warning("getWebNavigation() is deprecated - please use " +
-                     "viewSourceChrome.webNav instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  // The original implementation returned null if anything threw during
-  // the getting of the webNavigation.
-  try {
-    return viewSourceChrome.webNav;
-  } catch (e) {
-    return null;
-  }
-}
-
-function viewSource(url) {
-  Deprecated.warning("viewSource() is deprecated - please use " +
-                     "viewSourceChrome.loadURL() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.loadURL(url);
-}
-
-function ViewSourceGoToLine() {
-  Deprecated.warning("ViewSourceGoToLine() is deprecated - please use " +
-                     "viewSourceChrome.promptAndGoToLine() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.promptAndGoToLine();
-}
-
-function goToLine(line) {
-  Deprecated.warning("goToLine() is deprecated - please use " +
-                     "viewSourceChrome.goToLine() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.goToLine(line);
-}
-
-function BrowserForward(aEvent) {
-  Deprecated.warning("BrowserForward() is deprecated - please use " +
-                     "viewSourceChrome.goForward() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.goForward();
-}
-
-function BrowserBack(aEvent) {
-  Deprecated.warning("BrowserBack() is deprecated - please use " +
-                     "viewSourceChrome.goBack() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.goBack();
-}
-
-function UpdateBackForwardCommands() {
-  Deprecated.warning("UpdateBackForwardCommands() is deprecated - please use " +
-                     "viewSourceChrome.updateCommands() instead.",
-                     "https://developer.mozilla.org/en-US/Add-ons/Code_snippets/View_Source_for_XUL_Applications");
-  viewSourceChrome.updateCommands();
-}

deleted file mode 100644
--- a/toolkit/components/viewsource/content/viewSource.xul
+++ /dev/null
@@ -1,232 +0,0 @@
-<?xml version="1.0"?>
-# -*- Mode: HTML -*-
-# 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/.
-
-<?xml-stylesheet href="chrome://global/skin/" type="text/css"?>
-<?xml-stylesheet href="chrome://global/content/viewSource.css" type="text/css"?>
-<?xml-stylesheet href="chrome://mozapps/skin/viewsource/viewsource.css" type="text/css"?>
-<?xul-overlay href="chrome://global/content/editMenuOverlay.xul"?>
-
-<!DOCTYPE window [
-<!ENTITY % brandDTD SYSTEM "chrome://branding/locale/brand.dtd" >
-%brandDTD;
-<!ENTITY % sourceDTD SYSTEM "chrome://global/locale/viewSource.dtd" >
-%sourceDTD;
-<!ENTITY % charsetDTD SYSTEM "chrome://global/locale/charsetMenu.dtd" >
-%charsetDTD;
-]>
-
-<window id="viewSource"
-        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-        contenttitlesetting="true"
-        title="&mainWindow.title;"
-        titlemodifier="&mainWindow.titlemodifier;"
-        titlepreface="&mainWindow.preface;"
-        titlemenuseparator ="&mainWindow.titlemodifierseparator;"
-        windowtype="navigator:view-source"
-        width="640" height="480"
-        screenX="10" screenY="10"
-        persist="screenX screenY width height sizemode">
-
-  <script type="application/javascript" src="chrome://global/content/globalOverlay.js"/>
-  <script type="application/javascript" src="chrome://global/content/printUtils.js"/>
-  <script type="application/javascript" src="chrome://global/content/viewSource.js"/>
-  <script type="application/javascript" src="chrome://global/content/viewZoomOverlay.js"/>
-  <script type="application/javascript" src="chrome://global/content/contentAreaUtils.js"/>
-
-  <stringbundle id="viewSourceBundle" src="chrome://global/locale/viewSource.properties"/>
-
-  <command id="cmd_savePage" oncommand="ViewSourceSavePage();"/>
-  <command id="cmd_print" oncommand="PrintUtils.printWindow(gBrowser.outerWindowID, gBrowser);"/>
-  <command id="cmd_printpreview" oncommand="PrintUtils.printPreview(PrintPreviewListener);"/>
-  <command id="cmd_pagesetup" oncommand="PrintUtils.showPageSetup();"/>
-  <command id="cmd_close" oncommand="window.close();"/>
-  <commandset id="editMenuCommands"/>
-  <command id="cmd_find"
-           oncommand="document.getElementById('FindToolbar').onFindCommand();"/>
-  <command id="cmd_findAgain"
-           oncommand="document.getElementById('FindToolbar').onFindAgainCommand(false);"/>
-  <command id="cmd_findPrevious"
-           oncommand="document.getElementById('FindToolbar').onFindAgainCommand(true);"/>
-#ifdef XP_MACOSX
-  <command id="cmd_findSelection"
-           oncommand="document.getElementById('FindToolbar').onFindSelectionCommand();"/>
-#endif
-  <command id="cmd_reload" oncommand="viewSourceChrome.reload();"/>
-  <command id="cmd_goToLine" oncommand="viewSourceChrome.promptAndGoToLine();" disabled="true"/>
-  <command id="cmd_highlightSyntax" oncommand="viewSourceChrome.toggleSyntaxHighlighting();"/>
-  <command id="cmd_wrapLongLines" oncommand="viewSourceChrome.toggleWrapping();"/>
-  <command id="cmd_textZoomReduce" oncommand="ZoomManager.reduce();"/>
-  <command id="cmd_textZoomEnlarge" oncommand="ZoomManager.enlarge();"/>
-  <command id="cmd_textZoomReset" oncommand="ZoomManager.reset();"/>
-
-  <command id="Browser:Back" oncommand="viewSourceChrome.goBack()" observes="viewSourceNavigation"/>
-  <command id="Browser:Forward" oncommand="viewSourceChrome.goForward()" observes="viewSourceNavigation"/>
-
-  <broadcaster id="viewSourceNavigation"/>
-
-  <keyset id="editMenuKeys"/>
-  <keyset id="viewSourceKeys">
-    <key id="key_savePage" key="&savePageCmd.commandkey;" modifiers="accel" command="cmd_savePage"/>
-    <key id="key_print" key="&printCmd.commandkey;" modifiers="accel" command="cmd_print"/>
-    <key id="key_close" key="&closeCmd.commandkey;" modifiers="accel" command="cmd_close"/>
-    <key id="key_goToLine"     key="&goToLineCmd.commandkey;"  command="cmd_goToLine"  modifiers="accel"/>
-
-    <key id="key_textZoomEnlarge" key="&textEnlarge.commandkey;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomEnlarge2" key="&textEnlarge.commandkey2;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomEnlarge3" key="&textEnlarge.commandkey3;" command="cmd_textZoomEnlarge" modifiers="accel"/>
-    <key id="key_textZoomReduce"  key="&textReduce.commandkey;" command="cmd_textZoomReduce" modifiers="accel"/>
-    <key id="key_textZoomReduce2"  key="&textReduce.commandkey2;" command="cmd_textZoomReduce" modifiers="accel"/>
-    <key id="key_textZoomReset" key="&textReset.commandkey;" command="cmd_textZoomReset" modifiers="accel"/>
-    <key id="key_textZoomReset2" key="&textReset.commandkey2;" command="cmd_textZoomReset" modifiers="accel"/>
-
-    <key id="key_reload" key="&reloadCmd.commandkey;" command="cmd_reload" modifiers="accel"/>
-    <key key="&reloadCmd.commandkey;" command="cmd_reload" modifiers="accel,shift"/>
-    <key keycode="VK_F5" command="cmd_reload"/>
-    <key keycode="VK_F5" command="cmd_reload" modifiers="accel"/>
-    <key id="key_find" key="&findOnCmd.commandkey;" command="cmd_find" modifiers="accel"/>
-    <key id="key_findAgain" key="&findAgainCmd.commandkey;" command="cmd_findAgain" modifiers="accel"/>
-    <key id="key_findPrevious" key="&findAgainCmd.commandkey;" command="cmd_findPrevious" modifiers="accel,shift"/>
-#ifdef XP_MACOSX
-    <key id="key_findSelection" key="&findSelectionCmd.commandkey;" command="cmd_findSelection" modifiers="accel"/>
-#endif
-    <key keycode="&findAgainCmd.commandkey2;" command="cmd_findAgain"/>
-    <key keycode="&findAgainCmd.commandkey2;"  command="cmd_findPrevious" modifiers="shift"/>
-
-    <key keycode="VK_BACK" command="Browser:Back"/>
-    <key keycode="VK_BACK" command="Browser:Forward" modifiers="shift"/>
-#ifndef XP_MACOSX
-    <key id="goBackKb" keycode="VK_LEFT" command="Browser:Back" modifiers="alt"/>
-    <key id="goForwardKb" keycode="VK_RIGHT" command="Browser:Forward" modifiers="alt"/>
-#else
-    <key id="goBackKb" keycode="VK_LEFT" command="Browser:Back" modifiers="accel" />
-    <key id="goForwardKb" keycode="VK_RIGHT" command="Browser:Forward" modifiers="accel" />
-#endif
-#ifdef XP_UNIX
-    <key id="goBackKb2" key="&goBackCmd.commandKey;" command="Browser:Back" modifiers="accel"/>
-    <key id="goForwardKb2" key="&goForwardCmd.commandKey;" command="Browser:Forward" modifiers="accel"/>
-#endif
-
-  </keyset>
-
-  <tooltip id="aHTMLTooltip" page="true"/>
-
-  <menupopup id="viewSourceContextMenu">
-    <menuitem id="context-back"
-              label="&backCmd.label;"
-              accesskey="&backCmd.accesskey;"
-              command="Browser:Back"
-              observes="viewSourceNavigation"/>
-    <menuitem id="context-forward"
-              label="&forwardCmd.label;"
-              accesskey="&forwardCmd.accesskey;"
-              command="Browser:Forward"
-              observes="viewSourceNavigation"/>
-    <menuseparator observes="viewSourceNavigation"/>
-    <menuitem id="cMenu_findAgain"/>
-    <menuseparator/>
-    <menuitem id="cMenu_copy"/>
-    <menuitem id="context-copyLink"
-              label="&copyLinkCmd.label;"
-              accesskey="&copyLinkCmd.accesskey;"
-              oncommand="viewSourceChrome.onContextMenuCopyLinkOrEmail();"/>
-    <menuitem id="context-copyEmail"
-              label="&copyEmailCmd.label;"
-              accesskey="&copyEmailCmd.accesskey;"
-              oncommand="viewSourceChrome.onContextMenuCopyLinkOrEmail();"/>
-    <menuseparator/>
-    <menuitem id="cMenu_selectAll"/>
-  </menupopup>
-
-  <!-- Menu -->
-  <toolbox id="viewSource-toolbox">
-    <menubar id="viewSource-main-menubar">
-
-      <menu id="menu_file" label="&fileMenu.label;" accesskey="&fileMenu.accesskey;">
-        <menupopup id="menu_FilePopup">
-          <menuitem key="key_savePage" command="cmd_savePage" id="menu_savePage"
-                    label="&savePageCmd.label;" accesskey="&savePageCmd.accesskey;"/>
-          <menuitem command="cmd_pagesetup" id="menu_pageSetup"
-                    label="&pageSetupCmd.label;" accesskey="&pageSetupCmd.accesskey;"/>
-#ifndef XP_MACOSX
-          <menuitem command="cmd_printpreview" id="menu_printPreview"
-                    label="&printPreviewCmd.label;" accesskey="&printPreviewCmd.accesskey;"/>
-#endif
-          <menuitem key="key_print" command="cmd_print" id="menu_print"
-                    label="&printCmd.label;" accesskey="&printCmd.accesskey;"/>
-          <menuseparator/>
-          <menuitem key="key_close" command="cmd_close" id="menu_close"
-                    label="&closeCmd.label;" accesskey="&closeCmd.accesskey;"/>
-        </menupopup>
-      </menu>
-
-      <menu id="menu_edit">
-        <menupopup id="editmenu-popup">
-          <menuitem id="menu_undo"/>
-          <menuitem id="menu_redo"/>
-          <menuseparator/>
-          <menuitem id="menu_cut"/>
-          <menuitem id="menu_copy"/>
-          <menuitem id="menu_paste"/>
-          <menuitem id="menu_delete"/>
-          <menuseparator/>
-          <menuitem id="menu_selectAll"/>
-          <menuseparator/>
-          <menuitem id="menu_find"/>
-          <menuitem id="menu_findAgain"/>
-          <menuseparator/>
-          <menuitem id="menu_goToLine" key="key_goToLine" command="cmd_goToLine"
-                    label="&goToLineCmd.label;" accesskey="&goToLineCmd.accesskey;"/>
-        </menupopup>
-      </menu>
-
-      <menu id="menu_view" label="&viewMenu.label;" accesskey="&viewMenu.accesskey;">
-        <menupopup id="viewmenu-popup">
-          <menuitem id="menu_reload" command="cmd_reload" accesskey="&reloadCmd.accesskey;"
-                    label="&reloadCmd.label;" key="key_reload"/>
-          <menuseparator />
-          <menu id="viewTextZoomMenu" label="&menu_textSize.label;" accesskey="&menu_textSize.accesskey;">
-            <menupopup>
-              <menuitem id="menu_textEnlarge" command="cmd_textZoomEnlarge"
-                        label="&menu_textEnlarge.label;" accesskey="&menu_textEnlarge.accesskey;"
-                        key="key_textZoomEnlarge"/>
-              <menuitem id="menu_textReduce" command="cmd_textZoomReduce"
-                        label="&menu_textReduce.label;" accesskey="&menu_textReduce.accesskey;"
-                        key="key_textZoomReduce"/>
-              <menuseparator/>
-              <menuitem id="menu_textReset" command="cmd_textZoomReset"
-                        label="&menu_textReset.label;" accesskey="&menu_textReset.accesskey;"
-                        key="key_textZoomReset"/>
-            </menupopup>
-          </menu>
-
-          <!-- Charset Menu -->
-          <menu id="charsetMenu"
-                label="&charsetMenu2.label;"
-                accesskey="&charsetMenu2.accesskey;"
-                oncommand="viewSourceChrome.onSetCharacterSet(event);"
-                onpopupshowing="CharsetMenu.build(event.target);
-                                CharsetMenu.update(event.target, content.document.characterSet);">
-            <menupopup/>
-          </menu>
-          <menuseparator/>
-          <menuitem id="menu_wrapLongLines" type="checkbox" command="cmd_wrapLongLines"
-                    label="&menu_wrapLongLines.title;" accesskey="&menu_wrapLongLines.accesskey;"/>
-          <menuitem type="checkbox" id="menu_highlightSyntax" command="cmd_highlightSyntax"
-                    label="&menu_highlightSyntax.label;" accesskey="&menu_highlightSyntax.accesskey;"/>
-        </menupopup>
-      </menu>
-    </menubar>
-  </toolbox>
-
-  <vbox id="appcontent" flex="1">
-
-    <browser id="content" type="content" name="content" src="about:blank" flex="1"
-             primary="true"
-             context="viewSourceContextMenu" showcaret="true" tooltip="aHTMLTooltip" />
-    <findbar id="FindToolbar" browserid="content"/>
-  </vbox>
-
-</window>

--- a/toolkit/components/viewsource/content/viewSourceUtils.js
+++ b/toolkit/components/viewsource/content/viewSourceUtils.js
@@ -10,66 +10,72 @@
  *
  * This file silently depends on contentAreaUtils.js for
  * getDefaultFileName, getNormalizedLeafName and getDefaultExtension
  */
 
 ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 ChromeUtils.defineModuleGetter(this, "ViewSourceBrowser",
   "resource://gre/modules/ViewSourceBrowser.jsm");
-ChromeUtils.defineModuleGetter(this, "Deprecated",
-  "resource://gre/modules/Deprecated.jsm");
 ChromeUtils.defineModuleGetter(this, "PrivateBrowsingUtils",
   "resource://gre/modules/PrivateBrowsingUtils.jsm");
 ChromeUtils.defineModuleGetter(this, "Services",
   "resource://gre/modules/Services.jsm");
 
 var gViewSourceUtils = {
 
   mnsIWebBrowserPersist: Components.interfaces.nsIWebBrowserPersist,
   mnsIWebProgress: Components.interfaces.nsIWebProgress,
   mnsIWebPageDescriptor: Components.interfaces.nsIWebPageDescriptor,
 
   /**
    * Opens the view source window.
    *
-   * @param aArgsOrURL (required)
-   *        This is either an Object containing parameters, or a string
-   *        URL for the page we want to view the source of. In the latter
-   *        case we will be paying attention to the other parameters, as
-   *        we will be supporting the old API for this method.
-   *        If aArgsOrURL is an Object, the other parameters will be ignored.
-   *        aArgsOrURL as an Object can include the following properties:
+   * @param aArgs (required)
+   *        This Object can include the following properties:
    *
    *        URL (required):
    *          A string URL for the page we'd like to view the source of.
    *        browser (optional):
    *          The browser containing the document that we would like to view the
    *          source of. This is required if outerWindowID is passed.
    *        outerWindowID (optional):
    *          The outerWindowID of the content window containing the document that
    *          we want to view the source of. Pass this if you want to attempt to
    *          load the document source out of the network cache.
    *        lineNumber (optional):
    *          The line number to focus on once the source is loaded.
-   *
-   * @param aPageDescriptor (deprecated, optional)
-   *        Accepted for compatibility reasons, but is otherwise ignored.
-   * @param aDocument (deprecated, optional)
-   *        The content document we would like to view the source of. This
-   *        function will throw if aDocument is a CPOW.
-   * @param aLineNumber (deprecated, optional)
-   *        The line number to focus on once the source is loaded.
    */
-  viewSource(aArgsOrURL, aPageDescriptor, aDocument, aLineNumber) {
+  viewSource(aArgs) {
     if (Services.prefs.getBoolPref("view_source.editor.external")) {
-      this.openInExternalEditor(aArgsOrURL, aPageDescriptor, aDocument, aLineNumber);
-    } else {
-      this._openInInternalViewer(aArgsOrURL, aPageDescriptor, aDocument, aLineNumber);
+      this.openInExternalEditor(aArgs);
+      return;
+    }
+    // Try existing browsers first.
+    let browserWin = Services.wm.getMostRecentWindow("navigator:browser");
+    if (browserWin && browserWin.BrowserViewSourceOfDocument) {
+      browserWin.BrowserViewSourceOfDocument(aArgs);
+      return;
     }
+    // No browser window created yet, try to create one.
+    let utils = this;
+    Services.ww.registerNotification(function onOpen(subj, topic) {
+      if (subj.document.documentURI !== "about:blank" ||
+          topic !== "domwindowopened") {
+        return;
+      }
+      Services.ww.unregisterNotification(onOpen);
+      let win = subj.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
+                    .getInterface(Components.interfaces.nsIDOMWindow);
+      win.addEventListener("load", () => {
+        aArgs.viewSourceBrowser = win.gBrowser.selectedTab.linkedBrowser;
+        utils.viewSourceInBrowser(aArgs);
+      }, { once: true });
+    });
+    window.top.openUILinkIn("about:blank", "current");
   },
 
   /**
    * Displays view source in the provided <browser>.  This allows for non-window
    * display methods, such as a tab from Firefox.
    *
    * @param aArgs
    *        An object with the following properties:
@@ -101,76 +107,34 @@ var gViewSourceUtils = {
    * <browser>.  This allows for non-window display methods, such as a tab from
    * Firefox.
    *
    * @param aViewSourceInBrowser
    *        The browser containing the page to view the source of.
    * @param aTarget
    *        Set to the target node for MathML. Null for other types of elements.
    * @param aGetBrowserFn
-   *        If set, a function that will return a browser to open the source in.
-   *        If null, or this function returns null, opens the source in a new window.
+   *        A function that will return a browser to open the source in.
    */
   viewPartialSourceInBrowser(aViewSourceInBrowser, aTarget, aGetBrowserFn) {
     let mm = aViewSourceInBrowser.messageManager;
     mm.addMessageListener("ViewSource:GetSelectionDone", function gotSelection(message) {
       mm.removeMessageListener("ViewSource:GetSelectionDone", gotSelection);
 
       if (!message.data)
         return;
 
-      let browserToOpenIn = aGetBrowserFn ? aGetBrowserFn() : null;
-      if (browserToOpenIn) {
-        let viewSourceBrowser = new ViewSourceBrowser(browserToOpenIn);
-        viewSourceBrowser.loadViewSourceFromSelection(message.data.uri, message.data.drawSelection,
+      let viewSourceBrowser = new ViewSourceBrowser(aGetBrowserFn());
+      viewSourceBrowser.loadViewSourceFromSelection(message.data.uri, message.data.drawSelection,
                                                       message.data.baseURI);
-      } else {
-        window.openDialog("chrome://global/content/viewPartialSource.xul",
-                          "_blank", "all,dialog=no",
-                          {
-                            URI: message.data.uri,
-                            drawSelection: message.data.drawSelection,
-                            baseURI: message.data.baseURI,
-                            partial: true,
-                          });
-      }
     });
 
     mm.sendAsyncMessage("ViewSource:GetSelection", { }, { target: aTarget });
   },
 
-  // Opens the interval view source viewer
-  _openInInternalViewer(aArgsOrURL, aPageDescriptor, aDocument, aLineNumber) {
-    // try to open a view-source window while inheriting the charset (if any)
-    var charset = null;
-    var isForcedCharset = false;
-    if (aDocument) {
-      if (Components.utils.isCrossProcessWrapper(aDocument)) {
-        throw new Error("View Source cannot accept a CPOW as a document.");
-      }
-
-      charset = "charset=" + aDocument.characterSet;
-      try {
-        isForcedCharset =
-          aDocument.defaultView
-                   .QueryInterface(Components.interfaces.nsIInterfaceRequestor)
-                   .getInterface(Components.interfaces.nsIDOMWindowUtils)
-                   .docCharsetIsForced;
-      } catch (ex) {
-      }
-    }
-    Services.telemetry
-            .getHistogramById("VIEW_SOURCE_IN_WINDOW_OPENED_BOOLEAN")
-            .add(true);
-    openDialog("chrome://global/content/viewSource.xul",
-               "_blank",
-               "all,dialog=no",
-               aArgsOrURL, charset, aPageDescriptor, aLineNumber, isForcedCharset);
-  },
-
   buildEditorArgs(aPath, aLineNumber) {
     // Determine the command line arguments to pass to the editor.
     // We currently support a %LINE% placeholder which is set to the passed
     // line number (or to 0 if there's none)
     var editorArgs = [];
     var args = Services.prefs.getCharPref("view_source.editor.args");
     if (args) {
       args = args.replace("%LINE%", aLineNumber || "0");
@@ -181,89 +145,54 @@ var gViewSourceUtils = {
     }
     editorArgs.push(aPath);
     return editorArgs;
   },
 
   /**
    * Opens an external editor with the view source content.
    *
-   * @param aArgsOrURL (required)
-   *        This is either an Object containing parameters, or a string
-   *        URL for the page we want to view the source of. In the latter
-   *        case we will be paying attention to the other parameters, as
-   *        we will be supporting the old API for this method.
-   *        If aArgsOrURL is an Object, the other parameters will be ignored.
-   *        aArgsOrURL as an Object can include the following properties:
+   * @param aArgs (required)
+   *        This Object can include the following properties:
    *
    *        URL (required):
    *          A string URL for the page we'd like to view the source of.
    *        browser (optional):
    *          The browser containing the document that we would like to view the
    *          source of. This is required if outerWindowID is passed.
    *        outerWindowID (optional):
    *          The outerWindowID of the content window containing the document that
    *          we want to view the source of. Pass this if you want to attempt to
    *          load the document source out of the network cache.
    *        lineNumber (optional):
    *          The line number to focus on once the source is loaded.
    *
-   * @param aPageDescriptor (deprecated, optional)
-   *        Accepted for compatibility reasons, but is otherwise ignored.
-   * @param aDocument (deprecated, optional)
-   *        The content document we would like to view the source of. This
-   *        function will throw if aDocument is a CPOW.
-   * @param aLineNumber (deprecated, optional)
-   *        The line number to focus on once the source is loaded.
-   * @param aCallBack
+   * @param aCallBack (required)
    *        A function accepting two arguments:
    *          * result (true = success)
    *          * data object
-   *        The function defaults to opening an internal viewer if external
-   *        viewing fails.
    */
-  openInExternalEditor(aArgsOrURL, aPageDescriptor, aDocument,
-                                 aLineNumber, aCallBack) {
+  openInExternalEditor(aArgs, aCallBack) {
     let data;
-    if (typeof aArgsOrURL == "string") {
-      Deprecated.warning("The arguments you're passing to " +
-                         "openInExternalEditor are using an out-of-date API.",
-                         "https://developer.mozilla.org/en-US/Add-ons/" +
-                         "Code_snippets/View_Source_for_XUL_Applications");
-      if (Components.utils.isCrossProcessWrapper(aDocument)) {
-        throw new Error("View Source cannot accept a CPOW as a document.");
-      }
-      data = {
-        url: aArgsOrURL,
-        pageDescriptor: aPageDescriptor,
-        doc: aDocument,
-        lineNumber: aLineNumber,
-        isPrivate: false,
+    let { URL, browser, lineNumber } = aArgs;
+    data = {
+      url: URL,
+      lineNumber,
+      isPrivate: false,
+    };
+    if (browser) {
+      data.doc = {
+        characterSet: browser.characterSet,
+        contentType: browser.documentContentType,
+        title: browser.contentTitle,
       };
-      if (aDocument) {
-          data.isPrivate =
-            PrivateBrowsingUtils.isWindowPrivate(aDocument.defaultView);
-      }
-    } else {
-      let { URL, browser, lineNumber } = aArgsOrURL;
-      data = {
-        url: URL,
-        lineNumber,
-        isPrivate: false,
-      };
-      if (browser) {
-        data.doc = {
-          characterSet: browser.characterSet,
-          contentType: browser.documentContentType,
-          title: browser.contentTitle,
-        };
-        data.isPrivate = PrivateBrowsingUtils.isBrowserPrivate(browser);
-      }
+      data.isPrivate = PrivateBrowsingUtils.isBrowserPrivate(browser);
     }
 
+
     try {
       var editor = this.getExternalViewSourceEditor();
       if (!editor) {
         this.handleCallBack(aCallBack, false, data);
         return;
       }
 
       // make a uri
@@ -327,34 +256,22 @@ var gViewSourceUtils = {
       }
     } catch (ex) {
       // we failed loading it with the external editor.
       Components.utils.reportError(ex);
       this.handleCallBack(aCallBack, false, data);
     }
   },
 
-  // Default callback - opens the internal viewer if the external editor failed
-  internalViewerFallback(result, data) {
-    if (!result) {
-      this._openInInternalViewer(data.url, data.pageDescriptor, data.doc, data.lineNumber);
-    }
-  },
-
-  // Calls the callback, keeping in mind undefined or null values.
+  // Calls the callback, and record result in telemetry.
   handleCallBack(aCallBack, result, data) {
     Services.telemetry
             .getHistogramById("VIEW_SOURCE_EXTERNAL_RESULT_BOOLEAN")
             .add(result);
-    // if callback is undefined, default to the internal viewer
-    if (aCallBack === undefined) {
-      this.internalViewerFallback(result, data);
-    } else if (aCallBack) {
-      aCallBack(result, data);
-    }
+    aCallBack(result, data);
   },
 
   // Returns nsIProcess of the external view source editor or null
   getExternalViewSourceEditor() {
     try {
       let viewSourceAppPath =
         Services.prefs.getComplexValue("view_source.editor.path",
                                        Components.interfaces.nsIFile);

--- a/toolkit/components/viewsource/jar.mn
+++ b/toolkit/components/viewsource/jar.mn
@@ -1,14 +1,7 @@
 # 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/.
 
 toolkit.jar:
-#ifndef ANDROID
-  content/global/viewSource.css             (content/viewSource.css)
-  content/global/viewSource.js              (content/viewSource.js)
-* content/global/viewSource.xul             (content/viewSource.xul)
-  content/global/viewPartialSource.js       (content/viewPartialSource.js)
-* content/global/viewPartialSource.xul      (content/viewPartialSource.xul)
-#endif
   content/global/viewSourceUtils.js         (content/viewSourceUtils.js)
   content/global/viewSource-content.js      (content/viewSource-content.js)

--- a/toolkit/components/viewsource/test/browser/browser_contextmenu.js
+++ b/toolkit/components/viewsource/test/browser/browser_contextmenu.js
@@ -3,86 +3,63 @@
  */
 
 var source = "data:text/html,text<link%20href='http://example.com/'%20/>more%20text<a%20href='mailto:abc@def.ghi'>email</a>";
 var gViewSourceWindow, gContextMenu, gCopyLinkMenuItem, gCopyEmailMenuItem;
 
 var expectedData = [];
 
 add_task(async function() {
-  // Full source in view source window
-  let newWindow = await loadViewSourceWindow(source);
-  await SimpleTest.promiseFocus(newWindow);
+  // Full source in view source tab
+  let newTab = await openDocument(source);
+  await onViewSourceWindowOpen(window);
 
-  await onViewSourceWindowOpen(newWindow, false);
-
-  let contextMenu = gViewSourceWindow.document.getElementById("viewSourceContextMenu");
+  let contextMenu = document.getElementById("contentAreaContextMenu");
 
   for (let test of expectedData) {
-    await checkMenuItems(contextMenu, false, test[0], test[1], test[2], test[3]);
+    await checkMenuItems(contextMenu, test[0], test[1], test[2], test[3]);
   }
 
-  await new Promise(resolve => {
-    closeViewSourceWindow(newWindow, resolve);
-  });
+  gBrowser.removeTab(newTab);
 
   // Selection source in view source tab
   expectedData = [];
-  let newTab = await openDocumentSelect(source, "body");
-  await onViewSourceWindowOpen(window, true);
+  newTab = await openDocumentSelect(source, "body");
+  await onViewSourceWindowOpen(window);
 
   contextMenu = document.getElementById("contentAreaContextMenu");
 
   for (let test of expectedData) {
-    await checkMenuItems(contextMenu, true, test[0], test[1], test[2], test[3]);
+    await checkMenuItems(contextMenu, test[0], test[1], test[2], test[3]);
   }
 
   gBrowser.removeTab(newTab);
-
-  // Selection source in view source window
-  await pushPrefs(["view_source.tab", false]);
-
-  expectedData = [];
-  newWindow = await openDocumentSelect(source, "body");
-  await SimpleTest.promiseFocus(newWindow);
-
-  await onViewSourceWindowOpen(newWindow, false);
-
-  contextMenu = newWindow.document.getElementById("viewSourceContextMenu");
-
-  for (let test of expectedData) {
-    await checkMenuItems(contextMenu, false, test[0], test[1], test[2], test[3]);
-  }
-
-  await new Promise(resolve => {
-    closeViewSourceWindow(newWindow, resolve);
-  });
 });
 
-async function onViewSourceWindowOpen(aWindow, aIsTab) {
+async function onViewSourceWindowOpen(aWindow) {
   gViewSourceWindow = aWindow;
 
-  gCopyLinkMenuItem = aWindow.document.getElementById(aIsTab ? "context-copylink" : "context-copyLink");
-  gCopyEmailMenuItem = aWindow.document.getElementById(aIsTab ? "context-copyemail" : "context-copyEmail");
+  gCopyLinkMenuItem = aWindow.document.getElementById("context-copylink");
+  gCopyEmailMenuItem = aWindow.document.getElementById("context-copyemail");
 
-  let browser = aIsTab ? gBrowser.selectedBrowser : gViewSourceWindow.gBrowser;
+  let browser = gBrowser.selectedBrowser;
   await ContentTask.spawn(browser, null, async function(arg) {
     let tags = content.document.querySelectorAll("a[href]");
     Assert.equal(tags[0].href, "view-source:http://example.com/", "Link has correct href");
     Assert.equal(tags[1].href, "mailto:abc@def.ghi", "Link has correct href");
   });
 
   expectedData.push(["a[href]", true, false, "http://example.com/"]);
   expectedData.push(["a[href^=mailto]", false, true, "abc@def.ghi"]);
   expectedData.push(["span", false, false, null]);
 }
 
-async function checkMenuItems(contextMenu, isTab, selector, copyLinkExpected, copyEmailExpected, expectedClipboardContent) {
+async function checkMenuItems(contextMenu, selector, copyLinkExpected, copyEmailExpected, expectedClipboardContent) {
 
-  let browser = isTab ? gBrowser.selectedBrowser : gViewSourceWindow.gBrowser;
+  let browser = gBrowser.selectedBrowser;
   await ContentTask.spawn(browser, { selector }, async function(arg) {
     content.document.querySelector(arg.selector).scrollIntoView();
   });
 
   let popupShownPromise = BrowserTestUtils.waitForEvent(contextMenu, "popupshown");
   await BrowserTestUtils.synthesizeMouseAtCenter(selector,
           { type: "contextmenu", button: 2}, browser);
   await popupShownPromise;

--- a/toolkit/components/viewsource/test/browser/browser_gotoline.js
+++ b/toolkit/components/viewsource/test/browser/browser_gotoline.js
@@ -3,28 +3,31 @@
  */
 
 ChromeUtils.import("resource://testing-common/ContentTaskUtils.jsm", this);
 
 var content = "line 1\nline 2\nline 3";
 
 add_task(async function() {
   // First test with text with the text/html mimetype.
-  let win = await loadViewSourceWindow("data:text/html," + encodeURIComponent(content));
-  await checkViewSource(win);
-  await BrowserTestUtils.closeWindow(win);
+  let tab = await openDocument("data:text/html," + encodeURIComponent(content));
+  await checkViewSource(tab);
+  gBrowser.removeTab(tab);
 
-  win = await loadViewSourceWindow("data:text/plain," + encodeURIComponent(content));
-  await checkViewSource(win);
-  await BrowserTestUtils.closeWindow(win);
+  tab = await openDocument("data:text/plain," + encodeURIComponent(content));
+  await checkViewSource(tab);
+  gBrowser.removeTab(tab);
 });
 
-var checkViewSource = async function(aWindow) {
-  is(aWindow.gBrowser.contentDocument.body.textContent, content, "Correct content loaded");
+var checkViewSource = async function(aTab) {
+  let browser = aTab.linkedBrowser;
+  await ContentTask.spawn(browser, content, async function(text) {
+    is(content.document.body.textContent, text, "Correct content loaded");
+  });
 
   for (let i = 1; i <= 3; i++) {
-    aWindow.viewSourceChrome.goToLine(i);
-    await ContentTask.spawn(aWindow.gBrowser, i, async function(i) {
+    browser.messageManager.sendAsyncMessage("ViewSource:GoToLine", { lineNumber: i });
+    await ContentTask.spawn(browser, i, async function(i) {
       let selection = content.getSelection();
       Assert.equal(selection.toString(), "line " + i, "Correct text selected");
     });
   }
 };

--- a/toolkit/components/viewsource/test/browser/browser_open_docgroup.js
+++ b/toolkit/components/viewsource/test/browser/browser_open_docgroup.js
@@ -13,57 +13,25 @@ add_task(async function setup() {
     ],
   });
 });
 
 /**
  * Tests that we can open View Source in a tab.
  */
 add_task(async function test_view_source_in_tab() {
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      ["view_source.tab", true],
-    ],
-  });
-
   await BrowserTestUtils.withNewTab({
     gBrowser,
     url: "http://example.com",
   }, async function(browser) {
-    let sourceTab = await openViewSource(browser);
+    let sourceTab = await openViewSourceForBrowser(browser);
     let sourceBrowser = sourceTab.linkedBrowser;
 
     await ContentTask.spawn(sourceBrowser, null, async function() {
       Assert.equal(content.document.body.id, "viewsource",
                    "View source mode enabled");
     });
 
     await BrowserTestUtils.removeTab(sourceTab);
   });
 
   await SpecialPowers.popPrefEnv();
 });
-
-/**
- * Tests that we can open View Source in a window.
- */
-add_task(async function test_view_source_in_window() {
-  await SpecialPowers.pushPrefEnv({
-    set: [
-      ["view_source.tab", false],
-    ],
-  });
-
-  await BrowserTestUtils.withNewTab({
-    gBrowser,
-    url: "http://example.com",
-  }, async function(browser) {
-    let sourceWin = await openViewSource(browser);
-    await ContentTask.spawn(sourceWin.gBrowser, null, async function() {
-      Assert.equal(content.document.body.id, "viewsource",
-                   "View source mode enabled");
-    });
-
-    await closeViewSourceWindow(sourceWin);
-  });
-
-  await SpecialPowers.popPrefEnv();
-});

--- a/toolkit/components/viewsource/test/browser/browser_viewsourceprefs.js
+++ b/toolkit/components/viewsource/test/browser/browser_viewsourceprefs.js
@@ -13,123 +13,134 @@ add_task(async function setup() {
   });
 });
 
 add_task(async function() {
   await exercisePrefs(plaintextURL, false);
   await exercisePrefs(htmlURL, true);
 });
 
+async function removeChecked(browser, id) {
+  await ContentTask.spawn(browser, id, async function(id) {
+    let item = content.document.getElementById(id);
+    if (item.getAttribute("checked") == "false") {
+      item.removeAttribute("checked");
+    }
+  });
+}
+
+async function hasAttribute(browser, id, attribute) {
+  return ContentTask.spawn(browser, { id, attribute }, async function(arg) {
+    let item = content.document.getElementById(arg.id);
+    return item.hasAttribute(arg.attribute);
+  });
+}
+
 var exercisePrefs = async function(source, highlightable) {
-  let win = await loadViewSourceWindow(source);
-  let wrapMenuItem = win.document.getElementById("menu_wrapLongLines");
-  let syntaxMenuItem = win.document.getElementById("menu_highlightSyntax");
+  let tab = await openDocument(source);
+  let browser = tab.linkedBrowser;
+
+  const wrapMenuItem = "wrapLongLines";
+  const syntaxMenuItem = "highlightSyntax";
 
   // Strip checked="false" attributes, since we're not interested in them.
-  if (wrapMenuItem.getAttribute("checked") == "false") {
-    wrapMenuItem.removeAttribute("checked");
-  }
-  if (syntaxMenuItem.getAttribute("checked") == "false") {
-    syntaxMenuItem.removeAttribute("checked");
-  }
+  await removeChecked(browser, wrapMenuItem);
+  await removeChecked(browser, syntaxMenuItem);
 
   // Test the default states of these menu items.
-  is(wrapMenuItem.hasAttribute("checked"), false,
+  is(await hasAttribute(browser, wrapMenuItem, "checked"), false,
      "Wrap menu item not checked by default");
-  is(syntaxMenuItem.hasAttribute("checked"), true,
+  is(await hasAttribute(browser, syntaxMenuItem, "checked"), true,
      "Syntax menu item checked by default");
 
-  await checkStyle(win, "-moz-tab-size", 4);
-  await checkStyle(win, "white-space", "pre");
+  await checkStyle(browser, "-moz-tab-size", 4);
+  await checkStyle(browser, "white-space", "pre");
+
 
   // Next, test that the Wrap Long Lines menu item works.
   let prefReady = waitForPrefChange("view_source.wrap_long_lines");
-  simulateClick(wrapMenuItem);
-  is(wrapMenuItem.hasAttribute("checked"), true, "Wrap menu item checked");
+  await simulateClick(browser, wrapMenuItem);
+  is(await hasAttribute(browser, wrapMenuItem, "checked"), true, "Wrap menu item checked");
   await prefReady;
   is(SpecialPowers.getBoolPref("view_source.wrap_long_lines"), true, "Wrap pref set");
 
-  await checkStyle(win, "white-space", "pre-wrap");
+  await checkStyle(browser, "white-space", "pre-wrap");
 
   prefReady = waitForPrefChange("view_source.wrap_long_lines");
-  simulateClick(wrapMenuItem);
-  is(wrapMenuItem.hasAttribute("checked"), false, "Wrap menu item unchecked");
+  await simulateClick(browser, wrapMenuItem);
+  is(await hasAttribute(browser, wrapMenuItem, "checked"), false, "Wrap menu item unchecked");
   await prefReady;
   is(SpecialPowers.getBoolPref("view_source.wrap_long_lines"), false, "Wrap pref set");
-  await checkStyle(win, "white-space", "pre");
+  await checkStyle(browser, "white-space", "pre");
 
   // Check that the Syntax Highlighting menu item works.
   prefReady = waitForPrefChange("view_source.syntax_highlight");
-  simulateClick(syntaxMenuItem);
-  is(syntaxMenuItem.hasAttribute("checked"), false, "Syntax menu item unchecked");
+  await simulateClick(browser, syntaxMenuItem);
+  is(await hasAttribute(browser, syntaxMenuItem, "checked"), false, "Syntax menu item unchecked");
   await prefReady;
   is(SpecialPowers.getBoolPref("view_source.syntax_highlight"), false, "Syntax highlighting pref set");
-  await checkHighlight(win, false);
+  await checkHighlight(browser, false);
 
   prefReady = waitForPrefChange("view_source.syntax_highlight");
-  simulateClick(syntaxMenuItem);
-  is(syntaxMenuItem.hasAttribute("checked"), true, "Syntax menu item checked");
+  simulateClick(browser, syntaxMenuItem);
+  is(await hasAttribute(browser, syntaxMenuItem, "checked"), true, "Syntax menu item checked");
   await prefReady;
   is(SpecialPowers.getBoolPref("view_source.syntax_highlight"), true, "Syntax highlighting pref set");
-  await checkHighlight(win, highlightable);
-  await BrowserTestUtils.closeWindow(win);
+  await checkHighlight(browser, highlightable);
+  gBrowser.removeTab(tab);
 
   // Open a new view-source window to check that the prefs are obeyed.
   SpecialPowers.setIntPref("view_source.tab_size", 2);
   SpecialPowers.setBoolPref("view_source.wrap_long_lines", true);
   SpecialPowers.setBoolPref("view_source.syntax_highlight", false);
 
-  win = await loadViewSourceWindow(source);
-  wrapMenuItem = win.document.getElementById("menu_wrapLongLines");
-  syntaxMenuItem = win.document.getElementById("menu_highlightSyntax");
+  tab = await openDocument(source);
+  browser = tab.linkedBrowser;
 
   // Strip checked="false" attributes, since we're not interested in them.
-  if (wrapMenuItem.getAttribute("checked") == "false") {
-    wrapMenuItem.removeAttribute("checked");
-  }
-  if (syntaxMenuItem.getAttribute("checked") == "false") {
-    syntaxMenuItem.removeAttribute("checked");
-  }
+  await removeChecked(browser, wrapMenuItem);
+  await removeChecked(browser, syntaxMenuItem);
 
-  is(wrapMenuItem.hasAttribute("checked"), true, "Wrap menu item checked");
-  is(syntaxMenuItem.hasAttribute("checked"), false, "Syntax menu item unchecked");
-  await checkStyle(win, "-moz-tab-size", 2);
-  await checkStyle(win, "white-space", "pre-wrap");
-  await checkHighlight(win, false);
+  is(await hasAttribute(browser, wrapMenuItem, "checked"), true, "Wrap menu item checked");
+  is(await hasAttribute(browser, syntaxMenuItem, "checked"), false, "Syntax menu item unchecked");
+  await checkStyle(browser, "-moz-tab-size", 2);
+  await checkStyle(browser, "white-space", "pre-wrap");
+  await checkHighlight(browser, false);
 
   SpecialPowers.clearUserPref("view_source.tab_size");
   SpecialPowers.clearUserPref("view_source.wrap_long_lines");
   SpecialPowers.clearUserPref("view_source.syntax_highlight");
 
-  await BrowserTestUtils.closeWindow(win);
+  gBrowser.removeTab(tab);
 };
 
 // Simulate a menu item click, including toggling the checked state.
 // This saves us from opening the menu and trying to click on the item,
 // which doesn't work on Mac OS X.
-function simulateClick(aMenuItem) {
-  if (aMenuItem.hasAttribute("checked"))
-    aMenuItem.removeAttribute("checked");
-  else
-    aMenuItem.setAttribute("checked", "true");
+async function simulateClick(browser, id) {
+  return ContentTask.spawn(browser, id, async function(id) {
+    let item = content.document.getElementById(id);
+    if (item.hasAttribute("checked"))
+      item.removeAttribute("checked");
+    else
+      item.setAttribute("checked", "true");
 
-  aMenuItem.click();
+    item.click();
+  });
 }
 
-var checkStyle = async function(win, styleProperty, expected) {
-  let browser = win.gBrowser;
+var checkStyle = async function(browser, styleProperty, expected) {
   let value = await ContentTask.spawn(browser, styleProperty, async function(styleProperty) {
     let style = content.getComputedStyle(content.document.body);
     return style.getPropertyValue(styleProperty);
   });
   is(value, expected, "Correct value of " + styleProperty);
 };
 
-var checkHighlight = async function(win, expected) {
-  let browser = win.gBrowser;
+var checkHighlight = async function(browser, expected) {
   let highlighted = await ContentTask.spawn(browser, {}, async function() {
     let spans = content.document.getElementsByTagName("span");
     return Array.some(spans, (span) => {
       let style = content.getComputedStyle(span);
       return style.getPropertyValue("color") !== "rgb(0, 0, 0)";
     });
   });
   is(highlighted, expected, "Syntax highlighting " + (expected ? "on" : "off"));

--- a/toolkit/components/viewsource/test/browser/head.js
+++ b/toolkit/components/viewsource/test/browser/head.js
@@ -1,136 +1,95 @@
 /* Any copyright is dedicated to the Public Domain.
  * http://creativecommons.org/publicdomain/zero/1.0/
  */
 
 ChromeUtils.import("resource://gre/modules/PromiseUtils.jsm");
 ChromeUtils.import("resource://gre/modules/Preferences.jsm", this);
 
-const WINDOW_TYPE = "navigator:view-source";
-
-function openViewSourceWindow(aURI, aCallback) {
-  let viewSourceWindow = openDialog("chrome://global/content/viewSource.xul", null, null, aURI);
-  viewSourceWindow.addEventListener("pageshow", function pageShowHandler(event) {
-    // Wait for the inner window to load, not viewSourceWindow.
-    if (event.target.location == "view-source:" + aURI) {
-      info("View source window opened: " + event.target.location);
-      viewSourceWindow.removeEventListener("pageshow", pageShowHandler);
-      aCallback(viewSourceWindow);
-    }
-  });
-}
-
-function loadViewSourceWindow(URL) {
-  return new Promise((resolve) => {
-    openViewSourceWindow(URL, resolve);
-  });
-}
-
-function closeViewSourceWindow(aWindow, aCallback) {
-  return new Promise(resolve => {
-    Services.wm.addListener({
-      onCloseWindow() {
-        Services.wm.removeListener(this);
-        if (aCallback) {
-          executeSoon(aCallback);
-        }
-        resolve();
-      }
-    });
-    aWindow.close();
-  });
-}
-
-function testViewSourceWindow(aURI, aTestCallback, aCloseCallback) {
-  openViewSourceWindow(aURI, function(aWindow) {
-    aTestCallback(aWindow);
-    closeViewSourceWindow(aWindow, aCloseCallback);
-  });
-}
-
 /**
- * Wait for view source tab or window after calling given function to open it.
+ * Wait for view source tab after calling given function to open it.
  *
  * @param open - a function to open view source.
- * @returns the new tab or window which shows the source.
+ * @returns the new tab which shows the source.
  */
-async function waitForViewSourceTabOrWindow(open) {
+async function waitForViewSourceTab(open) {
   let sourceLoadedPromise;
-  let tabOrWindowPromise;
-  if (Services.prefs.getBoolPref("view_source.tab")) {
-    tabOrWindowPromise = new Promise(resolve => {
-      gBrowser.tabContainer.addEventListener("TabOpen", event => {
-        let tab = event.target;
-        sourceLoadedPromise = waitForSourceLoaded(tab);
-        resolve(tab);
-      }, { once: true });
-    });
-  } else {
-    tabOrWindowPromise = new Promise(resolve => {
-      let windowListener = {
-        onOpenWindow(xulWindow) {
-          let win = xulWindow.QueryInterface(Ci.nsIInterfaceRequestor)
-              .getInterface(Ci.nsIDOMWindow);
-          win.addEventListener("load", function() {
-            if (win.document.documentElement.getAttribute("windowtype") !=
-                WINDOW_TYPE) {
-              return;
-            }
-            // Found the window
-            sourceLoadedPromise = waitForSourceLoaded(win);
-            resolve(win);
-            Services.wm.removeListener(windowListener);
-          }, {once: true});
-        },
-        onCloseWindow() {},
-      };
-      Services.wm.addListener(windowListener);
-    });
-  }
+  let tabPromise;
+
+  tabPromise = new Promise(resolve => {
+    gBrowser.tabContainer.addEventListener("TabOpen", event => {
+      let tab = event.target;
+      sourceLoadedPromise = waitForSourceLoaded(tab);
+      resolve(tab);
+    }, { once: true });
+  });
 
   await open();
 
-  let tabOrWindow = await tabOrWindowPromise;
+  let tab = await tabPromise;
   await sourceLoadedPromise;
-
-  return tabOrWindow;
+  return tab;
 }
 
 /**
  * Opens view source for a browser.
  *
  * @param browser - the <xul:browser> to open view source for.
- * @returns the new tab or window which shows the source.
+ * @returns the new tab which shows the source.
  */
-function openViewSource(browser) {
-  return waitForViewSourceTabOrWindow(() => {
+function openViewSourceForBrowser(browser) {
+  return waitForViewSourceTab(() => {
     window.BrowserViewSource(browser);
   });
 }
 
 /**
- * Opens a view source tab / window for a selection (View Selection Source)
+ * Opens a view source tab. (View Source)
+ * within the currently selected browser in gBrowser.
+ *
+ * @returns the new tab which shows the source.
+ */
+async function openViewSource() {
+  let contentAreaContextMenuPopup =
+    document.getElementById("contentAreaContextMenu");
+  let popupShownPromise =
+    BrowserTestUtils.waitForEvent(contentAreaContextMenuPopup, "popupshown");
+  await BrowserTestUtils.synthesizeMouseAtCenter("body",
+          { type: "contextmenu", button: 2 }, gBrowser.selectedBrowser);
+  await popupShownPromise;
+
+  return waitForViewSourceTab(async () => {
+    let popupHiddenPromise =
+        BrowserTestUtils.waitForEvent(contentAreaContextMenuPopup, "popuphidden");
+    let item = document.getElementById("context-viewsource");
+    EventUtils.synthesizeMouseAtCenter(item, {});
+    await popupHiddenPromise;
+  });
+}
+
+/**
+ * Opens a view source tab for a selection (View Selection Source)
  * within the currently selected browser in gBrowser.
  *
  * @param aCSSSelector - used to specify a node within the selection to
  *                       view the source of. It is expected that this node is
  *                       within an existing selection.
- * @returns the new tab / window which shows the source.
+ * @returns the new tab which shows the source.
  */
 async function openViewPartialSource(aCSSSelector) {
   let contentAreaContextMenuPopup =
     document.getElementById("contentAreaContextMenu");
   let popupShownPromise =
     BrowserTestUtils.waitForEvent(contentAreaContextMenuPopup, "popupshown");
   await BrowserTestUtils.synthesizeMouseAtCenter(aCSSSelector,
           { type: "contextmenu", button: 2 }, gBrowser.selectedBrowser);
   await popupShownPromise;
 
-  return waitForViewSourceTabOrWindow(async () => {
+  return waitForViewSourceTab(async () => {
     let popupHiddenPromise =
         BrowserTestUtils.waitForEvent(contentAreaContextMenuPopup, "popuphidden");
     let item = document.getElementById("context-viewpartialsource-selection");
     EventUtils.synthesizeMouseAtCenter(item, {});
     await popupHiddenPromise;
   });
 }
 
@@ -151,70 +110,78 @@ async function openViewFrameSourceTab(aC
   await popupShownPromise;
 
   let frameContextMenu = document.getElementById("frame");
   popupShownPromise =
     BrowserTestUtils.waitForEvent(frameContextMenu, "popupshown");
   EventUtils.synthesizeMouseAtCenter(frameContextMenu, {});
   await popupShownPromise;
 
-  return waitForViewSourceTabOrWindow(async () => {
+  return waitForViewSourceTab(async () => {
     let popupHiddenPromise =
         BrowserTestUtils.waitForEvent(frameContextMenu, "popuphidden");
     let item = document.getElementById("context-viewframesource");
     EventUtils.synthesizeMouseAtCenter(item, {});
     await popupHiddenPromise;
   });
 }
 
-registerCleanupFunction(function() {
-  var windows = Services.wm.getEnumerator(WINDOW_TYPE);
-  ok(!windows.hasMoreElements(), "No remaining view source windows still open");
-  while (windows.hasMoreElements())
-    windows.getNext().close();
-});
-
 /**
- * For a given view source tab / window, wait for the source loading step to
+ * For a given view source tab, wait for the source loading step to
  * complete.
  */
-function waitForSourceLoaded(tabOrWindow) {
+function waitForSourceLoaded(tab) {
   return new Promise(resolve => {
-    let mm = tabOrWindow.messageManager ||
-             tabOrWindow.linkedBrowser.messageManager;
+    let mm = tab.linkedBrowser.messageManager;
     mm.addMessageListener("ViewSource:SourceLoaded", function sourceLoaded() {
       mm.removeMessageListener("ViewSource:SourceLoaded", sourceLoaded);
       setTimeout(resolve, 0);
     });
   });
 }
 
 /**
  * Open a new document in a new tab, select part of it, and view the source of
  * that selection. The document is not closed afterwards.
  *
  * @param aURI - url to load
  * @param aCSSSelector - used to specify a node to select. All of this node's
  *                       children will be selected.
- * @returns the new tab / window which shows the source.
+ * @returns the new tab which shows the source.
  */
 async function openDocumentSelect(aURI, aCSSSelector) {
   let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, aURI);
   registerCleanupFunction(function() {
     gBrowser.removeTab(tab);
   });
 
   await ContentTask.spawn(gBrowser.selectedBrowser, { selector: aCSSSelector }, async function(arg) {
     let element = content.document.querySelector(arg.selector);
     content.getSelection().selectAllChildren(element);
   });
 
   return openViewPartialSource(aCSSSelector);
 }
 
+/**
+ * Open a new document in a new tab and view the source of whole page.
+ * The document is not closed afterwards.
+ *
+ * @param aURI - url to load
+ * @returns the new tab which shows the source.
+ */
+async function openDocument(aURI) {
+  let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, aURI);
+  registerCleanupFunction(function() {
+    gBrowser.removeTab(tab);
+  });
+
+  return openViewSource();
+}
+
 function pushPrefs(...aPrefs) {
   return SpecialPowers.pushPrefEnv({"set": aPrefs});
 }
 
 function waitForPrefChange(pref) {
   let deferred = PromiseUtils.defer();
   let observer = () => {
     Preferences.ignore(pref, observer);

deleted file mode 100644
--- a/toolkit/locales/en-US/chrome/global/viewSource.dtd
+++ /dev/null
@@ -1,86 +0,0 @@
-<!-- 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/. -->
-
-<!-- extracted from content/viewSource.xul -->
-
-<!-- LOCALIZATION NOTE (mainWindow.title) : DONT_TRANSLATE --> 
-<!ENTITY mainWindow.title "&brandFullName;">
-<!-- LOCALIZATION NOTE (mainWindow.titlemodifier) : DONT_TRANSLATE --> 
-<!ENTITY mainWindow.titlemodifier "&brandFullName;">
-<!-- LOCALIZATION NOTE (mainWindow.titlemodifierseparator) : DONT_TRANSLATE -->
-<!ENTITY mainWindow.titlemodifierseparator " - ">
-<!ENTITY mainWindow.preface "Source of: ">
-
-<!ENTITY fileMenu.label "File">
-<!ENTITY fileMenu.accesskey "F">
-<!ENTITY savePageCmd.label "Save Page As…">
-<!ENTITY savePageCmd.accesskey "A">
-<!ENTITY savePageCmd.commandkey "S">
-<!ENTITY pageSetupCmd.label "Page Setup…">
-<!ENTITY pageSetupCmd.accesskey "u">
-<!ENTITY printPreviewCmd.label "Print Preview">
-<!ENTITY printPreviewCmd.accesskey "v">
-<!ENTITY printCmd.label "Print…">
-<!ENTITY printCmd.accesskey "P">
-<!ENTITY printCmd.commandkey "P">
-<!ENTITY closeCmd.label "Close">
-<!ENTITY closeCmd.accesskey "C">
-<!ENTITY closeCmd.commandkey "W">
-
-<!-- LOCALIZATION NOTE :
-textEnlarge.commandkey3, textReduce.commandkey2 and
-textReset.commandkey2 are alternative acceleration keys for zoom.
-If shift key is needed with your locale popular keyboard for them,
-you can use these alternative items. Otherwise, their values should be empty.  -->
-
-<!ENTITY textEnlarge.commandkey "+">
-<!ENTITY textEnlarge.commandkey2 "=">
-<!ENTITY textEnlarge.commandkey3 "">
-<!ENTITY textReduce.commandkey "-">
-<!ENTITY textReduce.commandkey2 "">
-<!ENTITY textReset.commandkey "0">
-<!ENTITY textReset.commandkey2 "">
-
-<!ENTITY goToLineCmd.label "Go to Line…">
-<!ENTITY goToLineCmd.accesskey "G">
-<!ENTITY goToLineCmd.commandkey "l">
-
-<!ENTITY viewMenu.label           "View">
-<!ENTITY viewMenu.accesskey       "V">
-<!ENTITY reloadCmd.label "Reload">
-<!ENTITY reloadCmd.accesskey "R">
-<!ENTITY reloadCmd.commandkey "r">
-<!ENTITY menu_wrapLongLines.title "Wrap Long Lines"> 
-<!ENTITY menu_wrapLongLines.accesskey "W">
-<!ENTITY menu_highlightSyntax.label "Syntax Highlighting">
-<!ENTITY menu_highlightSyntax.accesskey "H">
-<!ENTITY menu_textSize.label "Text Size">
-<!ENTITY menu_textSize.accesskey "Z">
-<!ENTITY menu_textEnlarge.label "Increase">
-<!ENTITY menu_textEnlarge.accesskey "I">
-<!ENTITY menu_textReduce.label "Decrease">
-<!ENTITY menu_textReduce.accesskey "D">
-<!ENTITY menu_textReset.label "Normal">
-<!ENTITY menu_textReset.accesskey "N">
-
-<!ENTITY findOnCmd.label     "Find in This Page…">
-<!ENTITY findOnCmd.accesskey "F">
-<!ENTITY findOnCmd.commandkey "f">
-<!ENTITY findAgainCmd.label  "Find Again">
-<!ENTITY findAgainCmd.accesskey "g">
-<!ENTITY findAgainCmd.commandkey "g">
-<!ENTITY findAgainCmd.commandkey2 "VK_F3">
-<!ENTITY findSelectionCmd.commandkey "e">
-
-<!ENTITY backCmd.label "Back">
-<!ENTITY backCmd.accesskey "B">
-<!ENTITY forwardCmd.label "Forward">
-<!ENTITY forwardCmd.accesskey "F">
-<!ENTITY goBackCmd.commandKey "[">
-<!ENTITY goForwardCmd.commandKey "]">
-
-<!ENTITY copyLinkCmd.label "Copy Link Location">
-<!ENTITY copyLinkCmd.accesskey "L">
-<!ENTITY copyEmailCmd.label "Copy Email Address">
-<!ENTITY copyEmailCmd.accesskey "E">

--- a/toolkit/locales/jar.mn
+++ b/toolkit/locales/jar.mn
@@ -69,17 +69,16 @@
 #endif
   locale/@AB_CD@/global/regionNames.properties          (%chrome/global/regionNames.properties)
   locale/@AB_CD@/global/resetProfile.dtd                (%chrome/global/resetProfile.dtd)
   locale/@AB_CD@/global/resetProfile.properties         (%chrome/global/resetProfile.properties)
   locale/@AB_CD@/global/dialog.properties               (%chrome/global/dialog.properties)
   locale/@AB_CD@/global/tree.dtd                        (%chrome/global/tree.dtd)
   locale/@AB_CD@/global/textcontext.dtd                 (%chrome/global/textcontext.dtd)
   locale/@AB_CD@/global/videocontrols.dtd               (%chrome/global/videocontrols.dtd)
-  locale/@AB_CD@/global/viewSource.dtd                  (%chrome/global/viewSource.dtd)
   locale/@AB_CD@/global/viewSource.properties           (%chrome/global/viewSource.properties)
   locale/@AB_CD@/global/wizard.dtd                      (%chrome/global/wizard.dtd)
   locale/@AB_CD@/global/wizard.properties               (%chrome/global/wizard.properties)
   locale/@AB_CD@/global/crashes.dtd                     (%crashreporter/crashes.dtd)
   locale/@AB_CD@/global/crashes.properties              (%crashreporter/crashes.properties)
 % locale global-platform @AB_CD@ %locale/@AB_CD@/global-platform/unix/ os=LikeUnix os=Android
 % locale global-platform @AB_CD@ %locale/@AB_CD@/global-platform/mac/ os=Darwin
 % locale global-platform @AB_CD@ %locale/@AB_CD@/global-platform/win/ os=WINNT

--- a/toolkit/themes/linux/mozapps/jar.mn
+++ b/toolkit/themes/linux/mozapps/jar.mn
@@ -5,15 +5,14 @@
 toolkit.jar:
 #include ../../shared/mozapps.inc.mn
   skin/classic/mozapps/downloads/downloadIcon.png          (downloads/downloadIcon.png)
 * skin/classic/mozapps/extensions/extensions.css           (extensions/extensions.css)
 * skin/classic/mozapps/extensions/newaddon.css             (extensions/newaddon.css)
   skin/classic/mozapps/extensions/heart.png                (extensions/heart.png)
   skin/classic/mozapps/profile/profileicon.png             (profile/profileicon.png)
   skin/classic/mozapps/update/updates.css                  (update/updates.css)
-  skin/classic/mozapps/viewsource/viewsource.css           (viewsource/viewsource.css)
 
 #if MOZ_BUILD_APP == browser
 [browser/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #elif MOZ_SEPARATE_MANIFEST_FOR_THEME_OVERRIDES
 [extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #endif

--- a/toolkit/themes/osx/mozapps/jar.mn
+++ b/toolkit/themes/osx/mozapps/jar.mn
@@ -19,17 +19,16 @@ toolkit.jar:
   skin/classic/mozapps/extensions/blocklist.css                   (extensions/blocklist.css)
 * skin/classic/mozapps/extensions/newaddon.css                    (extensions/newaddon.css)
   skin/classic/mozapps/plugins/pluginHelp-16.png                  (plugins/pluginHelp-16.png)
   skin/classic/mozapps/profile/profileicon.png                    (profile/profileicon.png)
   skin/classic/mozapps/profile/profileSelection.css               (profile/profileSelection.css)
   skin/classic/mozapps/profile/profileicon-selected.png           (profile/profileicon-selected.png)
   skin/classic/mozapps/update/buttons.png                         (update/buttons.png)
 * skin/classic/mozapps/update/updates.css                         (update/updates.css)
-  skin/classic/mozapps/viewsource/viewsource.css                  (viewsource/viewsource.css)
   skin/classic/mozapps/xpinstall/xpinstallConfirm.css             (extensions/xpinstallConfirm.css)
   skin/classic/mozapps/handling/handling.css                      (handling/handling.css)
 
 #if MOZ_BUILD_APP == browser
 [browser/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #elif MOZ_SEPARATE_MANIFEST_FOR_THEME_OVERRIDES
 [extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #endif
\ No newline at end of file

--- a/toolkit/themes/windows/mozapps/jar.mn
+++ b/toolkit/themes/windows/mozapps/jar.mn
@@ -5,15 +5,14 @@
 toolkit.jar:
 #include ../../shared/mozapps.inc.mn
   skin/classic/mozapps/downloads/downloadIcon.png            (downloads/downloadIcon.png)
 * skin/classic/mozapps/extensions/extensions.css             (extensions/extensions.css)
   skin/classic/mozapps/extensions/heart.png                  (extensions/heart.png)
 * skin/classic/mozapps/extensions/newaddon.css               (extensions/newaddon.css)
   skin/classic/mozapps/profile/profileicon.png               (profile/profileicon.png)
   skin/classic/mozapps/update/updates.css                    (update/updates.css)
-  skin/classic/mozapps/viewsource/viewsource.css             (viewsource/viewsource.css)
 
 #if MOZ_BUILD_APP == browser
 [browser/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #elif MOZ_SEPARATE_MANIFEST_FOR_THEME_OVERRIDES
 [extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}] chrome.jar:
 #endif