--- a/browser/base/content/test/general/browser.ini
+++ b/browser/base/content/test/general/browser.ini
@@ -382,17 +382,16 @@ skip-if = e10s && debug && os == "win" #
 [browser_save_video.js]
 [browser_save_video_frame.js]
 [browser_scope.js]
 [browser_contentSearchUI.js]
 support-files =
   contentSearchUI.html
   contentSearchUI.js
 [browser_selectpopup.js]
-run-if = e10s
 [browser_selectTabAtIndex.js]
 [browser_ssl_error_reports.js]
 [browser_star_hsts.js]
 [browser_subframe_favicons_not_used.js]
 [browser_syncui.js]
 [browser_tab_close_dependent_window.js]
 [browser_tabDrop.js]
 [browser_tabReorder.js]

--- a/browser/base/content/test/general/browser_selectpopup.js
+++ b/browser/base/content/test/general/browser_selectpopup.js
@@ -185,16 +185,24 @@ function* doSelectTests(contentType, dtd
   is((yield getChangeEvents()), isWindows ? 2 : 1, "Tab away from select with change - number of change events");
 
   is(selectPopup.lastChild.previousSibling.label, "Seven", "Spaces collapsed");
   is(selectPopup.lastChild.label, "\xA0\xA0Eight\xA0\xA0", "Non-breaking spaces not collapsed");
 
   yield BrowserTestUtils.removeTab(tab);
 }
 
+add_task(function* setup() {
+  yield SpecialPowers.pushPrefEnv({
+    "set": [
+      ["dom.select_popup_in_parent.enabled", true],
+    ]
+  });
+});
+
 add_task(function*() {
   yield doSelectTests("text/html", "");
 });
 
 add_task(function*() {
   yield doSelectTests("application/xhtml+xml", XHTML_DTD);
 });
 

--- a/layout/forms/nsListControlFrame.cpp
+++ b/layout/forms/nsListControlFrame.cpp
@@ -113,16 +113,22 @@ nsListControlFrame::nsListControlFrame(n
 }
 
 //---------------------------------------------------------
 nsListControlFrame::~nsListControlFrame()
 {
   mComboboxFrame = nullptr;
 }
 
+static bool ShouldFireDropDownEvent() {
+  return (XRE_IsContentProcess() &&
+          Preferences::GetBool("browser.tabs.remote.desktopbehavior", false)) ||
+         Preferences::GetBool("dom.select_popup_in_parent.enabled", false);
+}
+
 // for Bug 47302 (remove this comment later)
 void
 nsListControlFrame::DestroyFrom(nsIFrame* aDestructRoot)
 {
   // get the receiver interface from the browser button's content node
   ENSURE_TRUE(mContent);
 
   // Clear the frame pointer on our event listener, just in case the
@@ -136,18 +142,17 @@ nsListControlFrame::DestroyFrom(nsIFrame
                                       mEventListener, false);
   mContent->RemoveSystemEventListener(NS_LITERAL_STRING("mousedown"),
                                       mEventListener, false);
   mContent->RemoveSystemEventListener(NS_LITERAL_STRING("mouseup"),
                                       mEventListener, false);
   mContent->RemoveSystemEventListener(NS_LITERAL_STRING("mousemove"),
                                       mEventListener, false);
 
-  if (XRE_IsContentProcess() &&
-      Preferences::GetBool("browser.tabs.remote.desktopbehavior", false)) {
+  if (ShouldFireDropDownEvent()) {
     nsContentUtils::AddScriptRunner(
       new AsyncEventDispatcher(mContent,
                                NS_LITERAL_STRING("mozhidedropdown"), true,
                                true));
   }
 
   nsFormControlFrame::RegUnRegAccessKey(static_cast<nsIFrame*>(this), false);
   nsHTMLScrollFrame::DestroyFrom(aDestructRoot);
@@ -1775,18 +1780,17 @@ nsListControlFrame::GetIndexFromDOMEvent
   }
 
   return NS_ERROR_FAILURE;
 }
 
 static bool
 FireShowDropDownEvent(nsIContent* aContent, bool aShow, bool aIsSourceTouchEvent)
 {
-  if (XRE_IsContentProcess() &&
-      Preferences::GetBool("browser.tabs.remote.desktopbehavior", false)) {
+  if (ShouldFireDropDownEvent()) {
     nsString eventName;
     if (aShow) {
       eventName = aIsSourceTouchEvent ? NS_LITERAL_STRING("mozshowdropdown-sourcetouch") :
                                         NS_LITERAL_STRING("mozshowdropdown");
     } else {
       eventName = NS_LITERAL_STRING("mozhidedropdown");
     }
     nsContentUtils::DispatchChromeEvent(aContent->OwnerDoc(), aContent,

--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -112,16 +112,17 @@ pref("offline-apps.quota.warn",        5
 // cache compression turned off for now - see bug #715198
 pref("browser.cache.compression_level", 0);
 
 // Don't show "Open with" option on download dialog if true.
 pref("browser.download.forbid_open_with", false);
 
 // Whether or not testing features are enabled.
 pref("dom.quotaManager.testing", false);
+pref("dom.select_popup_in_parent.enabled", false);
 
 // Whether or not indexedDB is enabled.
 pref("dom.indexedDB.enabled", true);
 // Whether or not indexedDB experimental features are enabled.
 pref("dom.indexedDB.experimental", false);
 // Enable indexedDB logging.
 pref("dom.indexedDB.logging.enabled", true);
 // Detailed output in log messages.

--- a/toolkit/content/browser-content.js
+++ b/toolkit/content/browser-content.js
@@ -10,16 +10,18 @@ var Cr = Components.results;
 
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyModuleGetter(this, "ReaderMode",
   "resource://gre/modules/ReaderMode.jsm");
 XPCOMUtils.defineLazyModuleGetter(this, "BrowserUtils",
   "resource://gre/modules/BrowserUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "SelectContentHelper",
+  "resource://gre/modules/SelectContentHelper.jsm");
 
 var global = this;
 
 
 // Lazily load the finder code
 addMessageListener("Finder:Initialize", function () {
   let {RemoteFinderListener} = Cu.import("resource://gre/modules/RemoteFinder.jsm", {});
   new RemoteFinderListener(global);
@@ -1755,8 +1757,26 @@ let DateTimePickerListener = {
       }
       default:
         break;
     }
   },
 }
 
 DateTimePickerListener.init();
+
+addEventListener("mozshowdropdown", event => {
+  if (!event.isTrusted)
+    return;
+
+  if (!SelectContentHelper.open) {
+    new SelectContentHelper(event.target, {isOpenedViaTouch: false}, this);
+  }
+});
+
+addEventListener("mozshowdropdown-sourcetouch", event => {
+  if (!event.isTrusted)
+    return;
+
+  if (!SelectContentHelper.open) {
+    new SelectContentHelper(event.target, {isOpenedViaTouch: true}, this);
+  }
+});

--- a/toolkit/content/jar.mn
+++ b/toolkit/content/jar.mn
@@ -56,17 +56,16 @@ toolkit.jar:
    content/global/filepicker.properties
    content/global/globalOverlay.js
    content/global/mozilla.xhtml
    content/global/process-content.js
    content/global/resetProfile.css
    content/global/resetProfile.js
    content/global/resetProfile.xul
    content/global/resetProfileProgress.xul
-   content/global/select-child.js
    content/global/TopLevelVideoDocument.js
    content/global/timepicker.xhtml
    content/global/treeUtils.js
    content/global/viewZoomOverlay.js
    content/global/bindings/autocomplete.xml    (widgets/autocomplete.xml)
    content/global/bindings/browser.xml         (widgets/browser.xml)
    content/global/bindings/button.xml          (widgets/button.xml)
    content/global/bindings/checkbox.xml        (widgets/checkbox.xml)

deleted file mode 100644
--- a/toolkit/content/select-child.js
+++ /dev/null
@@ -1,26 +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/. */
-
-Components.utils.import("resource://gre/modules/XPCOMUtils.jsm");
-
-XPCOMUtils.defineLazyModuleGetter(this, "SelectContentHelper",
-                                  "resource://gre/modules/SelectContentHelper.jsm");
-
-addEventListener("mozshowdropdown", event => {
-  if (!event.isTrusted)
-    return;
-
-  if (!SelectContentHelper.open) {
-    new SelectContentHelper(event.target, {isOpenedViaTouch: false}, this);
-  }
-});
-
-addEventListener("mozshowdropdown-sourcetouch", event => {
-  if (!event.isTrusted)
-    return;
-
-  if (!SelectContentHelper.open) {
-    new SelectContentHelper(event.target, {isOpenedViaTouch: true}, this);
-  }
-});

--- a/toolkit/content/widgets/browser.xml
+++ b/toolkit/content/widgets/browser.xml
@@ -946,16 +946,22 @@
 
           if (this.messageManager) {
             this.messageManager.addMessageListener("PopupBlocking:UpdateBlockedPopups", this);
             this.messageManager.addMessageListener("Autoscroll:Start", this);
             this.messageManager.addMessageListener("Autoscroll:Cancel", this);
             this.messageManager.addMessageListener("AudioPlayback:Start", this);
             this.messageManager.addMessageListener("AudioPlayback:Stop", this);
             this.messageManager.addMessageListener("AudioPlayback:Block", this);
+
+            if (this.hasAttribute("selectmenulist")) {
+              this.messageManager.addMessageListener("Forms:ShowDropDown", this);
+              this.messageManager.addMessageListener("Forms:HideDropDown", this);
+            }
+
           }
         ]]>
       </constructor>
 
       <destructor>
         <![CDATA[
           this.destroy();
         ]]>
@@ -964,16 +970,21 @@
       <!-- This is necessary because the destructor doesn't always get called when
            we are removed from a tabbrowser. This will be explicitly called by tabbrowser.
 
            Note: this function is overriden in remote-browser.xml, so any clean-up that
            also applies to browser.isRemoteBrowser = true must be duplicated there. -->
       <method name="destroy">
         <body>
           <![CDATA[
+          // Make sure that any open select is closed.
+          if (this._selectParentHelper) {
+            let menulist = document.getElementById(this.getAttribute("selectmenulist"));
+            this._selectParentHelper.hide(menulist, this);
+          }
           if (this.mDestroyed)
             return;
           this.mDestroyed = true;
 
           if (this.docShell && this.webNavigation.sessionHistory) {
             var os = Components.classes["@mozilla.org/observer-service;1"]
                                .getService(Components.interfaces.nsIObserverService);
             try {
@@ -1035,16 +1046,37 @@
               this.audioPlaybackStarted();
               break;
             case "AudioPlayback:Stop":
               this.audioPlaybackStopped();
               break;
             case "AudioPlayback:Block":
               this.audioPlaybackBlocked();
               break;
+            case "Forms:ShowDropDown": {
+              if (!this._selectParentHelper) {
+                this._selectParentHelper =
+                  Cu.import("resource://gre/modules/SelectParentHelper.jsm", {}).SelectParentHelper;
+              }
+
+              let menulist = document.getElementById(this.getAttribute("selectmenulist"));
+              menulist.menupopup.style.direction = data.direction;
+              this._selectParentHelper.populate(menulist, data.options, data.selectedIndex, this._fullZoom);
+              this._selectParentHelper.open(this, menulist, data.rect);
+              break;
+            }
+
+            case "Forms:HideDropDown": {
+              if (this._selectParentHelper) {
+                let menulist = document.getElementById(this.getAttribute("selectmenulist"));
+                this._selectParentHelper.hide(menulist, this);
+              }
+              break;
+            }
+
           }
           return undefined;
         ]]></body>
       </method>
 
       <method name="receiveMessage">
         <parameter name="aMessage"/>
         <body><![CDATA[

--- a/toolkit/content/widgets/remote-browser.xml
+++ b/toolkit/content/widgets/remote-browser.xml
@@ -384,17 +384,16 @@
           this.messageManager.addMessageListener("DOMFullscreen:RequestExit", this);
           this.messageManager.addMessageListener("DOMFullscreen:RequestRollback", this);
           this.messageManager.addMessageListener("MozApplicationManifest", this);
           this.messageManager.loadFrameScript("chrome://global/content/browser-child.js", true);
 
           if (this.hasAttribute("selectmenulist")) {
             this.messageManager.addMessageListener("Forms:ShowDropDown", this);
             this.messageManager.addMessageListener("Forms:HideDropDown", this);
-            this.messageManager.loadFrameScript("chrome://global/content/select-child.js", true);
           }
 
           if (!this.hasAttribute("disablehistory")) {
             Services.obs.addObserver(this, "browser:purge-session-history", true);
           }
 
           let jsm = "resource://gre/modules/RemoteController.jsm";
           let RemoteController = Components.utils.import(jsm, {}).RemoteController;
@@ -495,24 +494,16 @@
 
             case "ZoomChangeUsingMouseWheel": {
               let event = document.createEvent("Events");
               event.initEvent("ZoomChangeUsingMouseWheel", true, false);
               this.dispatchEvent(event);
               break;
             }
 
-            case "Forms:HideDropDown": {
-              if (this._selectParentHelper) {
-                let menulist = document.getElementById(this.getAttribute("selectmenulist"));
-                this._selectParentHelper.hide(menulist, this);
-              }
-              break;
-            }
-
             case "DOMFullscreen:RequestExit": {
               let windowUtils = window.QueryInterface(Components.interfaces.nsIInterfaceRequestor)
                                       .getInterface(Components.interfaces.nsIDOMWindowUtils);
               windowUtils.exitFullscreen();
               break;
             }
 
             case "DOMFullscreen:RequestRollback": {