--- a/devtools/client/framework/ToolboxProcess.jsm
+++ b/devtools/client/framework/ToolboxProcess.jsm
@@ -8,25 +8,25 @@
 
 const DBG_XUL = "chrome://devtools/content/framework/toolbox-process-window.xul";
 const CHROME_DEBUGGER_PROFILE_NAME = "chrome_debugger_profile";
 
 const { require, DevToolsLoader } = ChromeUtils.import("resource://devtools/shared/Loader.jsm", {});
 const { XPCOMUtils } = require("resource://gre/modules/XPCOMUtils.jsm");
 
 ChromeUtils.defineModuleGetter(this, "Subprocess", "resource://gre/modules/Subprocess.jsm");
+ChromeUtils.defineModuleGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm");
+
 XPCOMUtils.defineLazyGetter(this, "Telemetry", function() {
   return require("devtools/client/shared/telemetry");
 });
 XPCOMUtils.defineLazyGetter(this, "EventEmitter", function() {
   return require("devtools/shared/event-emitter");
 });
-XPCOMUtils.defineLazyGetter(this, "system", function() {
-  return require("devtools/shared/system");
-});
+
 const promise = require("promise");
 const Services = require("Services");
 
 this.EXPORTED_SYMBOLS = ["BrowserToolboxProcess"];
 
 var processes = new Set();
 
 /**
@@ -284,17 +284,17 @@ BrowserToolboxProcess.prototype = {
 
     // During local development, incremental builds can trigger the main process
     // to clear its startup cache with the "flag file" .purgecaches, but this
     // file is removed during app startup time, so we aren't able to know if it
     // was present in order to also clear the child profile's startup cache as
     // well.
     //
     // As an approximation of "isLocalBuild", check for an unofficial build.
-    if (!system.constants.MOZILLA_OFFICIAL) {
+    if (!AppConstants.MOZILLA_OFFICIAL) {
       args.push("-purgecaches");
     }
 
     this._dbgProcessPromise = Subprocess.call({
       command,
       arguments: args,
       environmentAppend: true,
       stderr: "stdout",

--- a/devtools/client/framework/toolbox-hosts.js
+++ b/devtools/client/framework/toolbox-hosts.js
@@ -7,17 +7,17 @@
 "use strict";
 
 const EventEmitter = require("devtools/shared/event-emitter");
 const promise = require("promise");
 const defer = require("devtools/shared/defer");
 const Services = require("Services");
 const {DOMHelpers} = require("resource://devtools/client/shared/DOMHelpers.jsm");
 
-loader.lazyRequireGetter(this, "system", "devtools/shared/system");
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
 loader.lazyRequireGetter(this, "gDevToolsBrowser", "devtools/client/framework/devtools-browser", true);
 
 /* A host should always allow this much space for the page to be displayed.
  * There is also a min-height on the browser, but we still don't want to set
  * frame.height to be larger than that, since it can cause problems with
  * resizing the toolbox and panel layout. */
 const MIN_PAGE_SIZE = 25;
 
@@ -290,17 +290,17 @@ WindowHost.prototype = {
     let win = Services.ww.openWindow(null, this.WINDOW_URL, "_blank",
                                      flags, null);
 
     let frameLoad = () => {
       win.removeEventListener("load", frameLoad, true);
       win.focus();
 
       let key;
-      if (system.constants.platform === "macosx") {
+      if (AppConstants.platform === "macosx") {
         key = win.document.getElementById("toolbox-key-toggle-osx");
       } else {
         key = win.document.getElementById("toolbox-key-toggle");
       }
       key.removeAttribute("disabled");
 
       this.frame = win.document.getElementById("toolbox-iframe");
       this.emit("ready", this.frame);

--- a/devtools/client/framework/toolbox-options.js
+++ b/devtools/client/framework/toolbox-options.js
@@ -6,17 +6,17 @@
 
 const Services = require("Services");
 const defer = require("devtools/shared/defer");
 const {gDevTools} = require("devtools/client/framework/devtools");
 
 const {LocalizationHelper} = require("devtools/shared/l10n");
 const L10N = new LocalizationHelper("devtools/client/locales/toolbox.properties");
 
-loader.lazyRequireGetter(this, "system", "devtools/shared/system");
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
 
 exports.OptionsPanel = OptionsPanel;
 
 function GetPref(name) {
   let type = Services.prefs.getPrefType(name);
   switch (type) {
     case Services.prefs.PREF_STRING:
       return Services.prefs.getCharPref(name);
@@ -305,17 +305,17 @@ OptionsPanel.prototype = {
 
     this.updateCurrentTheme();
   },
 
   /**
    * Add common preferences enabled only on Nightly.
    */
   setupNightlyOptions: function() {
-    let isNightly = system.constants.NIGHTLY_BUILD;
+    let isNightly = AppConstants.NIGHTLY_BUILD;
     if (!isNightly) {
       return;
     }
 
     // Labels for these new buttons are nightly only and mostly intended for working on
     // devtools.
     let prefDefinitions = [{
       pref: "devtools.webconsole.new-frontend-enabled",

--- a/devtools/client/inspector/rules/test/browser_rules_edit-property-increments.js
+++ b/devtools/client/inspector/rules/test/browser_rules_edit-property-increments.js
@@ -5,17 +5,17 @@
 "use strict";
 
 // Test that increasing/decreasing values in rule view using
 // arrow keys works correctly.
 
 // Bug 1275446 - This test happen to hit the default timeout on linux32
 requestLongerTimeout(2);
 
-loader.lazyRequireGetter(this, "system", "devtools/shared/system");
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
 
 const TEST_URI = `
   <style>
     #test {
       margin-top: 0px;
       padding-top: 0px;
       color: #000000;
       background-color: #000000;
@@ -289,17 +289,17 @@ function* testIncrement(editor, options,
   key = options.down ? "VK_DOWN" : "VK_UP";
   if (options.pageDown) {
     key = "VK_PAGE_DOWN";
   } else if (options.pageUp) {
     key = "VK_PAGE_UP";
   }
 
   let smallIncrementKey = {ctrlKey: options.ctrl};
-  if (system.constants.platform === "macosx") {
+  if (AppConstants.platform === "macosx") {
     smallIncrementKey = {altKey: options.alt};
   }
 
   EventUtils.synthesizeKey(key, {...smallIncrementKey, shiftKey: options.shift},
     view.styleWindow);
 
   yield onKeyUp;
 
@@ -308,13 +308,13 @@ function* testIncrement(editor, options,
     view.debounce.flush();
     yield onRuleViewChanged;
   }
 
   is(input.value, options.end, "Value changed to " + options.end);
 }
 
 function getSmallIncrementKey() {
-  if (system.constants.platform === "macosx") {
+  if (AppConstants.platform === "macosx") {
     return { alt: true };
   }
   return { ctrl: true };
 }

--- a/devtools/client/shared/inplace-editor.js
+++ b/devtools/client/shared/inplace-editor.js
@@ -22,17 +22,17 @@
  */
 
 "use strict";
 
 const Services = require("Services");
 const focusManager = Services.focus;
 const {KeyCodes} = require("devtools/client/shared/keycodes");
 
-loader.lazyRequireGetter(this, "system", "devtools/shared/system");
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
 
 const HTML_NS = "http://www.w3.org/1999/xhtml";
 const CONTENT_TYPES = {
   PLAIN_TEXT: 0,
   CSS_VALUE: 1,
   CSS_MIXED: 2,
   CSS_PROPERTY: 3,
 };
@@ -1204,17 +1204,17 @@ InplaceEditor.prototype = {
     this.popup.hidePopup();
   },
 
   /**
    * Get the increment/decrement step to use for the provided key event.
    */
   _getIncrement: function(event) {
     const getSmallIncrementKey = (evt) => {
-      if (system.constants.platform === "macosx") {
+      if (AppConstants.platform === "macosx") {
         return evt.altKey;
       }
       return evt.ctrlKey;
     };
 
     const largeIncrement = 100;
     const mediumIncrement = 10;
     const smallIncrement = 0.1;

rename from devtools/client/shared/webpack/shims/system-stub.js
rename to devtools/client/shared/webpack/shims/app-constants-stub.js
--- a/devtools/client/shared/webpack/shims/system-stub.js
+++ b/devtools/client/shared/webpack/shims/app-constants-stub.js
@@ -6,12 +6,12 @@
 
 var platform = "";
 
 if (/Mac OS X/.test(window.navigator.userAgent)) {
   platform = "macosx";
 }
 
 module.exports = {
-  constants: {
-    platform: platform
+  AppConstants: {
+    platform
   }
 };

--- a/devtools/client/webconsole/new-webconsole.js
+++ b/devtools/client/webconsole/new-webconsole.js
@@ -11,17 +11,19 @@ const EventEmitter = require("devtools/s
 const promise = require("promise");
 const defer = require("devtools/shared/defer");
 const Services = require("Services");
 const { gDevTools } = require("devtools/client/framework/devtools");
 const { JSTerm } = require("devtools/client/webconsole/jsterm");
 const { WebConsoleConnectionProxy } = require("devtools/client/webconsole/webconsole-connection-proxy");
 const KeyShortcuts = require("devtools/client/shared/key-shortcuts");
 const { l10n } = require("devtools/client/webconsole/new-console-output/utils/messages");
-const system = require("devtools/shared/system");
+
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
+
 const ZoomKeys = require("devtools/client/shared/zoom-keys");
 
 const PREF_MESSAGE_TIMESTAMP = "devtools.webconsole.timestampMessages";
 const PREF_PERSISTLOG = "devtools.webconsole.persistlog";
 const PREF_SIDEBAR_ENABLED = "devtools.webconsole.sidebarToggle";
 
 // XXX: This file is incomplete (see bug 1326937).
 // It's used when loading the webconsole with devtools-launchpad, but will ultimately be
@@ -235,31 +237,31 @@ NewWebConsoleFrame.prototype = {
 
     shortcuts.on(l10n.getStr("webconsole.find.key"),
                  event => {
                    this.filterBox.focus();
                    event.preventDefault();
                  });
 
     let clearShortcut;
-    if (system.constants.platform === "macosx") {
+    if (AppConstants.platform === "macosx") {
       clearShortcut = l10n.getStr("webconsole.clear.keyOSX");
     } else {
       clearShortcut = l10n.getStr("webconsole.clear.key");
     }
 
     shortcuts.on(clearShortcut, () => this.jsterm.clearOutput(true));
 
     if (this.isBrowserConsole) {
       shortcuts.on(l10n.getStr("webconsole.close.key"),
                    this.window.top.close.bind(this.window.top));
 
       ZoomKeys.register(this.window);
 
-      if (!system.constants.MOZILLA_OFFICIAL) {
+      if (!AppConstants.MOZILLA_OFFICIAL) {
         // In local builds, inject the "quick restart" shortcut.
         // This script expects to have Services on the global and we haven't yet imported
         // it into the window, so assign it.
         this.window.Services = Services;
         Services.scriptloader.loadSubScript(
           "chrome://browser/content/browser-development-helpers.js", this.window);
         shortcuts.on("CmdOrCtrl+Alt+R", this.window.DevelopmentHelpers.quickRestart);
       }

--- a/devtools/client/webconsole/webconsole.js
+++ b/devtools/client/webconsole/webconsole.js
@@ -20,22 +20,22 @@ const promise = require("promise");
 const defer = require("devtools/shared/defer");
 const Services = require("Services");
 const Telemetry = require("devtools/client/shared/telemetry");
 const {PrefObserver} = require("devtools/client/shared/prefs");
 
 loader.lazyServiceGetter(this, "clipboardHelper",
                          "@mozilla.org/widget/clipboardhelper;1",
                          "nsIClipboardHelper");
+loader.lazyRequireGetter(this, "AppConstants", "resource://gre/modules/AppConstants.jsm", true);
 loader.lazyRequireGetter(this, "EventEmitter", "devtools/shared/event-emitter");
 loader.lazyRequireGetter(this, "ConsoleOutput", "devtools/client/webconsole/console-output", true);
 loader.lazyRequireGetter(this, "Messages", "devtools/client/webconsole/console-output", true);
 loader.lazyRequireGetter(this, "EnvironmentClient", "devtools/shared/client/environment-client");
 loader.lazyRequireGetter(this, "ObjectClient", "devtools/shared/client/object-client");
-loader.lazyRequireGetter(this, "system", "devtools/shared/system");
 loader.lazyRequireGetter(this, "JSTerm", "devtools/client/webconsole/jsterm", true);
 loader.lazyRequireGetter(this, "gSequenceId", "devtools/client/webconsole/jsterm", true);
 loader.lazyImporter(this, "VariablesView", "resource://devtools/client/shared/widgets/VariablesView.jsm");
 loader.lazyImporter(this, "VariablesViewController", "resource://devtools/client/shared/widgets/VariablesViewController.jsm");
 loader.lazyRequireGetter(this, "gDevTools", "devtools/client/framework/devtools", true);
 loader.lazyRequireGetter(this, "KeyShortcuts", "devtools/client/shared/key-shortcuts");
 loader.lazyRequireGetter(this, "ZoomKeys", "devtools/client/shared/zoom-keys");
 loader.lazyRequireGetter(this, "WebConsoleConnectionProxy", "devtools/client/webconsole/webconsole-connection-proxy", true);
@@ -637,17 +637,17 @@ WebConsoleFrame.prototype = {
 
     shortcuts.on(l10n.getStr("webconsole.find.key"),
                  event => {
                    this.filterBox.focus();
                    event.preventDefault();
                  });
 
     let clearShortcut;
-    if (system.constants.platform === "macosx") {
+    if (AppConstants.platform === "macosx") {
       clearShortcut = l10n.getStr("webconsole.clear.keyOSX");
     } else {
       clearShortcut = l10n.getStr("webconsole.clear.key");
     }
     shortcuts.on(clearShortcut,
                  () => this.jsterm.clearOutput(true));
 
     if (this.isBrowserConsole) {

--- a/devtools/client/webconsole/webpack.config.js
+++ b/devtools/client/webconsole/webpack.config.js
@@ -82,17 +82,17 @@ webpackConfig.resolve = {
 
     "devtools/client/shared/vendor/immutable": "immutable",
     "devtools/client/shared/vendor/react": "react",
     "devtools/client/shared/vendor/react-dom": "react-dom",
     "devtools/client/shared/vendor/react-redux": "react-redux",
     "devtools/client/shared/vendor/redux": "redux",
     "devtools/client/shared/vendor/reselect": "reselect",
 
-    "devtools/shared/system": path.join(__dirname, "../../client/shared/webpack/shims/system-stub"),
+    "resource://gre/modules/AppConstants.jsm": path.join(__dirname, "../../client/shared/webpack/shims/app-constants-stub"),
 
     "devtools/client/framework/devtools": path.join(__dirname, "../../client/shared/webpack/shims/framework-devtools-shim"),
     "devtools/client/framework/menu": "devtools-modules/src/menu",
     "devtools/client/sourceeditor/editor": "devtools-source-editor/src/source-editor",
 
     "devtools/client/shared/zoom-keys": "devtools-modules/src/zoom-keys",
 
     "devtools/shared/fronts/timeline": path.join(__dirname, "../../client/shared/webpack/shims/fronts-timeline-shim"),

--- a/devtools/shared/system.js
+++ b/devtools/shared/system.js
@@ -288,9 +288,8 @@ function getSetting(name) {
     deferred.reject(new Error("No settings service"));
   }
   return deferred.promise;
 }
 
 exports.getSystemInfo = getSystemInfo;
 exports.getSetting = getSetting;
 exports.getScreenDimensions = getScreenDimensions;
-exports.constants = AppConstants;