--- a/browser/app/profile/firefox.js
+++ b/browser/app/profile/firefox.js
@@ -271,17 +271,16 @@ pref("browser.slowStartup.timeThreshold"
 pref("browser.slowStartup.maxSamples", 5);
 
 // This url, if changed, MUST continue to point to an https url. Pulling arbitrary content to inject into
 // this page over http opens us up to a man-in-the-middle attack that we'd rather not face. If you are a downstream
 // repackager of this code using an alternate snippet url, please keep your users safe
 pref("browser.aboutHomeSnippets.updateUrl", "https://snippets.cdn.mozilla.net/%STARTPAGE_VERSION%/%NAME%/%VERSION%/%APPBUILDID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/");
 
 pref("browser.enable_automatic_image_resizing", true);
-pref("browser.casting.enabled", false);
 pref("browser.chrome.site_icons", true);
 pref("browser.chrome.favicons", true);
 // browser.warnOnQuit == false will override all other possible prompts when quitting or restarting
 pref("browser.warnOnQuit", true);
 // browser.showQuitWarning specifically controls the quit warning dialog. We
 // might still show the window closing dialog with showQuitWarning == false.
 pref("browser.showQuitWarning", false);
 pref("browser.fullscreen.autohide", true);

--- a/browser/base/content/browser-context.inc
+++ b/browser/base/content/browser-context.inc
@@ -236,21 +236,16 @@
       <menuitem id="context-video-saveimage"
                 accesskey="&videoSaveImage.accesskey;"
                 label="&videoSaveImage.label;"
                 oncommand="gContextMenu.saveVideoFrameAsImage();"/>
       <menuitem id="context-sendvideo"
                 label="&emailVideoCmd.label;"
                 accesskey="&emailVideoCmd.accesskey;"
                 oncommand="gContextMenu.sendMedia();"/>
-      <menu id="context-castvideo"
-                label="&castVideoCmd.label;"
-                accesskey="&castVideoCmd.accesskey;">
-        <menupopup id="context-castvideo-popup" onpopupshowing="gContextMenu.populateCastVideoMenu(this)"/>
-      </menu>
       <menuitem id="context-sendaudio"
                 label="&emailAudioCmd.label;"
                 accesskey="&emailAudioCmd.accesskey;"
                 oncommand="gContextMenu.sendMedia();"/>
       <menuitem id="context-ctp-play"
                 label="&playPluginCmd.label;"
                 accesskey="&playPluginCmd.accesskey;"
                 oncommand="gContextMenu.playPlugin();"/>

--- a/browser/base/content/browser-menubar.inc
+++ b/browser/base/content/browser-menubar.inc
@@ -468,18 +468,17 @@
       </menu>
       <menuseparator id="bookmarksMenuItemsSeparator"/>
       <!-- Bookmarks menu items -->
     </menupopup>
   </menu>
 
             <menu id="tools-menu"
                   label="&toolsMenu.label;"
-                  accesskey="&toolsMenu.accesskey;"
-                  onpopupshowing="mirrorShow(this)">
+                  accesskey="&toolsMenu.accesskey;">
               <menupopup id="menu_ToolsPopup">
               <menuitem id="menu_openDownloads"
                         label="&downloads.label;"
                         accesskey="&downloads.accesskey;"
                         key="key_openDownloads"
                         command="Tools:Downloads"/>
               <menuitem id="menu_openAddons"
                         label="&addons.label;"
@@ -515,23 +514,16 @@
               </menu>
               <menuitem id="menu_pageInfo"
                         accesskey="&pageInfoCmd.accesskey;"
                         label="&pageInfoCmd.label;"
 #ifndef XP_WIN
                         key="key_viewInfo"
 #endif
                         command="View:PageInfo"/>
-              <menu id="menu_mirrorTabCmd"
-                    hidden="true"
-                    accesskey="&mirrorTabCmd.accesskey;"
-                    label="&mirrorTabCmd.label;">
-                <menupopup id="menu_mirrorTab-popup"
-                           onpopupshowing="populateMirrorTabMenu(this)"/>
-              </menu>
 #ifndef XP_UNIX
               <menuseparator id="prefSep"/>
               <menuitem id="menu_preferences"
                         label="&preferencesCmd2.label;"
                         accesskey="&preferencesCmd2.accesskey;"
                         oncommand="openPreferences(undefined, {origin: 'menubar'});"/>
 #endif
               </menupopup>

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -21,17 +21,16 @@ XPCOMUtils.defineLazyGetter(this, "exten
 
 // lazy module getters
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   AboutHome: "resource:///modules/AboutHome.jsm",
   BrowserUITelemetry: "resource:///modules/BrowserUITelemetry.jsm",
   BrowserUsageTelemetry: "resource:///modules/BrowserUsageTelemetry.jsm",
   BrowserUtils: "resource://gre/modules/BrowserUtils.jsm",
-  CastingApps: "resource:///modules/CastingApps.jsm",
   CharsetMenu: "resource://gre/modules/CharsetMenu.jsm",
   Color: "resource://gre/modules/Color.jsm",
   ContentSearch: "resource:///modules/ContentSearch.jsm",
   ContextualIdentityService: "resource://gre/modules/ContextualIdentityService.jsm",
   CustomizableUI: "resource:///modules/CustomizableUI.jsm",
   Deprecated: "resource://gre/modules/Deprecated.jsm",
   DownloadsCommon: "resource:///modules/DownloadsCommon.jsm",
   E10SUtils: "resource:///modules/E10SUtils.jsm",
@@ -3311,45 +3310,16 @@ function getDefaultHomePage() {
   }
   return url;
 }
 
 function BrowserFullScreen() {
   window.fullScreen = !window.fullScreen;
 }
 
-function mirrorShow(popup) {
-  let services = [];
-  if (Services.prefs.getBoolPref("browser.casting.enabled")) {
-    services = CastingApps.getServicesForMirroring();
-  }
-  popup.ownerDocument.getElementById("menu_mirrorTabCmd").hidden = !services.length;
-}
-
-function mirrorMenuItemClicked(event) {
-  gBrowser.selectedBrowser.messageManager.sendAsyncMessage("SecondScreen:tab-mirror",
-                                                           {service: event.originalTarget._service});
-}
-
-function populateMirrorTabMenu(popup) {
-  popup.innerHTML = null;
-  if (!Services.prefs.getBoolPref("browser.casting.enabled")) {
-    return;
-  }
-  let doc = popup.ownerDocument;
-  let services = CastingApps.getServicesForMirroring();
-  services.forEach(service => {
-    let item = doc.createElement("menuitem");
-    item.setAttribute("label", service.friendlyName);
-    item._service = service;
-    item.addEventListener("command", mirrorMenuItemClicked);
-    popup.appendChild(item);
-  });
-}
-
 function getWebNavigation() {
   return gBrowser.webNavigation;
 }
 
 function BrowserReloadWithFlags(reloadFlags) {
   let url = gBrowser.currentURI.spec;
   if (gBrowser.updateBrowserRemotenessByURL(gBrowser.selectedBrowser, url)) {
     // If the remoteness has changed, the new browser doesn't have any

--- a/browser/base/content/nsContextMenu.js
+++ b/browser/base/content/nsContextMenu.js
@@ -273,31 +273,20 @@ nsContextMenu.prototype = {
     this.showItem("context-savevideo", this.onVideo);
     this.showItem("context-saveaudio", this.onAudio);
     this.showItem("context-video-saveimage", this.onVideo);
     this.setItemAttr("context-savevideo", "disabled", !this.mediaURL);
     this.setItemAttr("context-saveaudio", "disabled", !this.mediaURL);
     // Send media URL (but not for canvas, since it's a big data: URL)
     this.showItem("context-sendimage", this.onImage);
     this.showItem("context-sendvideo", this.onVideo);
-    this.showItem("context-castvideo", this.onVideo);
     this.showItem("context-sendaudio", this.onAudio);
     let mediaIsBlob = this.mediaURL.startsWith("blob:");
     this.setItemAttr("context-sendvideo", "disabled", !this.mediaURL || mediaIsBlob);
     this.setItemAttr("context-sendaudio", "disabled", !this.mediaURL || mediaIsBlob);
-    let shouldShowCast = Services.prefs.getBoolPref("browser.casting.enabled");
-    // getServicesForVideo alone would be sufficient here (it depends on
-    // SimpleServiceDiscovery.services), but SimpleServiceDiscovery is guaranteed
-    // to be already loaded, since we load it on startup in nsBrowserGlue,
-    // and CastingApps isn't, so check SimpleServiceDiscovery.services first
-    // to avoid needing to load CastingApps.jsm if we don't need to.
-    shouldShowCast = shouldShowCast && this.mediaURL &&
-                     SimpleServiceDiscovery.services.length > 0 &&
-                     CastingApps.getServicesForVideo(this.target).length > 0;
-    this.setItemAttr("context-castvideo", "disabled", !shouldShowCast);
   },
 
   initViewItems: function CM_initViewItems() {
     // View source is always OK, unless in directory listing.
     this.showItem("context-viewpartialsource-selection",
                   this.isContentSelected);
     this.showItem("context-viewpartialsource-mathml",
                   this.onMathML && !this.isContentSelected);
@@ -1538,35 +1527,16 @@ nsContextMenu.prototype = {
     if (this.onCanvas || this.onImage)
         this.sendMedia();
   },
 
   sendMedia() {
     MailIntegration.sendMessage(this.mediaURL, "");
   },
 
-  castVideo() {
-    CastingApps.openExternal(this.target, window);
-  },
-
-  populateCastVideoMenu(popup) {
-    let videoEl = this.target;
-    popup.innerHTML = null;
-    let doc = popup.ownerDocument;
-    let services = CastingApps.getServicesForVideo(videoEl);
-    services.forEach(service => {
-      let item = doc.createElement("menuitem");
-      item.setAttribute("label", service.friendlyName);
-      item.addEventListener("command", event => {
-        CastingApps.sendVideoToService(videoEl, service);
-      });
-      popup.appendChild(item);
-    });
-  },
-
   playPlugin() {
     gPluginHandler.contextMenuCommand(this.browser, this.target, "play");
   },
 
   hidePlugin() {
     gPluginHandler.contextMenuCommand(this.browser, this.target, "hide");
   },
 

--- a/browser/base/content/tab-content.js
+++ b/browser/base/content/tab-content.js
@@ -88,29 +88,16 @@ addMessageListener("Browser:Reload", fun
   } catch (e) {
   }
 });
 
 addMessageListener("MixedContent:ReenableProtection", function() {
   docShell.mixedContentChannel = null;
 });
 
-addMessageListener("SecondScreen:tab-mirror", function(message) {
-  if (!Services.prefs.getBoolPref("browser.casting.enabled")) {
-    return;
-  }
-  let app = SimpleServiceDiscovery.findAppForService(message.data.service);
-  if (app) {
-    let width = content.innerWidth;
-    let height = content.innerHeight;
-    let viewport = {cssWidth: width, cssHeight: height, width, height};
-    app.mirror(function() {}, content, viewport, function() {}, content);
-  }
-});
-
 var AboutHomeListener = {
   init(chromeGlobal) {
     chromeGlobal.addEventListener("AboutHomeLoad", this, false, true);
   },
 
   get isAboutHome() {
     return content.document.documentURI.toLowerCase() == "about:home";
   },

--- a/browser/base/content/test/general/browser_contextmenu.js
+++ b/browser/base/content/test/general/browser_contextmenu.js
@@ -174,18 +174,16 @@ add_task(async function test_video_ok() 
      "context-video-fullscreen",   true,
      "---",                        null,
      "context-viewvideo",          true,
      "context-copyvideourl",       true,
      "---",                        null,
      "context-savevideo",          true,
      "context-video-saveimage",    true,
      "context-sendvideo",          true,
-     "context-castvideo",          null,
-       [], null
     ]
   );
 });
 
 add_task(async function test_audio_in_video() {
   await test_contextmenu("#test-audio-in-video",
     ["context-media-play",         true,
      "context-media-mute",         true,
@@ -221,18 +219,16 @@ add_task(async function test_video_bad()
      "context-video-fullscreen",   false,
      "---",                        null,
      "context-viewvideo",          true,
      "context-copyvideourl",       true,
      "---",                        null,
      "context-savevideo",          true,
      "context-video-saveimage",    false,
      "context-sendvideo",          true,
-     "context-castvideo",          null,
-       [], null
     ]
   );
 });
 
 add_task(async function test_video_bad2() {
   await test_contextmenu("#test-video-bad2",
     ["context-media-play",         false,
      "context-media-mute",         false,
@@ -247,18 +243,16 @@ add_task(async function test_video_bad2(
      "context-video-fullscreen",   false,
      "---",                        null,
      "context-viewvideo",          false,
      "context-copyvideourl",       false,
      "---",                        null,
      "context-savevideo",          false,
      "context-video-saveimage",    false,
      "context-sendvideo",          false,
-     "context-castvideo",          null,
-       [], null
     ]
   );
 });
 
 add_task(async function test_iframe() {
   await test_contextmenu("#test-iframe",
     ["context-navigation", null,
          ["context-back",         false,
@@ -309,18 +303,16 @@ add_task(async function test_video_in_if
      "context-video-fullscreen",   true,
      "---",                        null,
      "context-viewvideo",          true,
      "context-copyvideourl",       true,
      "---",                        null,
      "context-savevideo",          true,
      "context-video-saveimage",    true,
      "context-sendvideo",          true,
-     "context-castvideo",          null,
-       [], null,
      "frame",                null,
          ["context-showonlythisframe", true,
           "context-openframeintab",    true,
           "context-openframe",         true,
           "---",                       null,
           "context-reloadframe",       true,
           "---",                       null,
           "context-bookmarkframe",     true,

--- a/browser/components/nsBrowserGlue.js
+++ b/browser/components/nsBrowserGlue.js
@@ -989,45 +989,21 @@ BrowserGlue.prototype = {
     BrowserUsageTelemetry.uninit();
 
     PageThumbs.uninit();
     NewTabUtils.uninit();
     AutoCompletePopup.uninit();
     DateTimePickerHelper.uninit();
   },
 
-  _initServiceDiscovery() {
-    if (!Services.prefs.getBoolPref("browser.casting.enabled")) {
-      return;
-    }
-    var rokuDevice = {
-      id: "roku:ecp",
-      target: "roku:ecp",
-      factory(aService) {
-        Cu.import("resource://gre/modules/RokuApp.jsm");
-        return new RokuApp(aService);
-      },
-      types: ["video/mp4"],
-      extensions: ["mp4"]
-    };
-
-    // Register targets
-    SimpleServiceDiscovery.registerDevice(rokuDevice);
-
-    // Search for devices continuously every 120 seconds
-    SimpleServiceDiscovery.search(120 * 1000);
-  },
-
   // All initial windows have opened.
   _onWindowsRestored: function BG__onWindowsRestored() {
     BrowserUsageTelemetry.init();
     BrowserUITelemetry.init();
 
-    this._initServiceDiscovery();
-
     // Show update notification, if needed.
     if (Services.prefs.prefHasUserValue("app.update.postupdate"))
       this._showUpdateNotification();
 
     ExtensionsUI.init();
 
     let signingRequired;
     if (AppConstants.MOZ_REQUIRE_SIGNING) {

--- a/browser/locales/en-US/chrome/browser/browser.dtd
+++ b/browser/locales/en-US/chrome/browser/browser.dtd
@@ -567,18 +567,16 @@ These should match what Safari and other
 <!ENTITY saveVideoCmd.label           "Save Video As…">
 <!ENTITY saveVideoCmd.accesskey       "v">
 <!ENTITY saveAudioCmd.label           "Save Audio As…">
 <!ENTITY saveAudioCmd.accesskey       "v">
 <!ENTITY emailImageCmd.label          "Email Image…">
 <!ENTITY emailImageCmd.accesskey      "g">
 <!ENTITY emailVideoCmd.label          "Email Video…">
 <!ENTITY emailVideoCmd.accesskey      "a">
-<!ENTITY castVideoCmd.label           "Send Video To Device">
-<!ENTITY castVideoCmd.accesskey       "e">
 <!ENTITY emailAudioCmd.label          "Email Audio…">
 <!ENTITY emailAudioCmd.accesskey      "a">
 <!ENTITY playPluginCmd.label          "Activate this plugin">
 <!ENTITY playPluginCmd.accesskey      "c">
 <!ENTITY hidePluginCmd.label          "Hide this plugin">
 <!ENTITY hidePluginCmd.accesskey      "H">
 <!ENTITY copyLinkCmd.label            "Copy Link Location">
 <!ENTITY copyLinkCmd.accesskey        "a">

--- a/browser/modules/moz.build
+++ b/browser/modules/moz.build
@@ -123,17 +123,16 @@ BROWSER_CHROME_MANIFESTS += ['test/brows
 XPCSHELL_TESTS_MANIFESTS += ['test/unit/xpcshell.ini']
 
 EXTRA_JS_MODULES += [
     'AboutHome.jsm',
     'AboutNewTab.jsm',
     'AttributionCode.jsm',
     'BrowserUITelemetry.jsm',
     'BrowserUsageTelemetry.jsm',
-    'CastingApps.jsm',
     'ContentClick.jsm',
     'ContentCrashHandlers.jsm',
     'ContentLinkHandler.jsm',
     'ContentObservers.js',
     'ContentSearch.jsm',
     'ContentWebRTC.jsm',
     'DirectoryLinksProvider.jsm',
     'E10SUtils.jsm',

--- a/testing/mochitest/runrobocop.py
+++ b/testing/mochitest/runrobocop.py
@@ -221,17 +221,16 @@ class RobocopTestRunner(MochitestDesktop
 
            This is similar to buildProfile in runtestsremote.py.
         """
         self.options.extraPrefs.append('browser.search.suggest.enabled=true')
         self.options.extraPrefs.append('browser.search.suggest.prompted=true')
         self.options.extraPrefs.append('layout.css.devPixelsPerPx=1.0')
         self.options.extraPrefs.append('browser.chrome.dynamictoolbar=false')
         self.options.extraPrefs.append('browser.snippets.enabled=false')
-        self.options.extraPrefs.append('browser.casting.enabled=true')
         self.options.extraPrefs.append('extensions.autoupdate.enabled=false')
 
         # Override the telemetry init delay for integration testing.
         self.options.extraPrefs.append('toolkit.telemetry.initDelay=1')
 
         self.options.extensionsToExclude.extend([
             'mochikit@mozilla.org',
             'worker-test@mozilla.org.xpi',