--- a/testing/marionette/components/marionette.js
+++ b/testing/marionette/components/marionette.js
@@ -6,16 +6,19 @@
 
 const {Constructor: CC, interfaces: Ci, utils: Cu, classes: Cc} = Components;
 
 Cu.import("resource://gre/modules/Log.jsm");
 Cu.import("resource://gre/modules/Preferences.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
+XPCOMUtils.defineLazyServiceGetter(
+    this, "env", "@mozilla.org/process/environment;1", "nsIEnvironment");
+
 const MARIONETTE_CONTRACT_ID = "@mozilla.org/marionette;1";
 const MARIONETTE_CID = Components.ID("{786a1369-dca5-4adc-8486-33d23c88010a}");
 
 const PREF_ENABLED = "marionette.enabled";
 const PREF_ENABLED_FALLBACK = "marionette.defaultPrefs.enabled";
 const PREF_PORT = "marionette.port";
 const PREF_PORT_FALLBACK = "marionette.defaultPrefs.port";
 const PREF_LOG_LEVEL = "marionette.log.level";
@@ -40,29 +43,34 @@ const LOG_LEVELS = new class extends Map
     let s = new String(level).toLowerCase();
     if (!this.has(s)) {
       return DEFAULT_LOG_LEVEL;
     }
     return super.get(s);
   }
 };
 
+// Complements -marionette flag for starting the Marionette server.
+// We also set this if Marionette is running in order to start the server
+// again after a Firefox restart.
+const ENV_ENABLED = "MOZ_MARIONETTE";
+
 // Besides starting based on existing prefs in a profile and a command
 // line flag, we also support inheriting prefs out of an env var, and to
 // start Marionette that way.
 //
 // This allows marionette prefs to persist when we do a restart into
 // a different profile in order to test things like Firefox refresh.
 // The environment variable itself, if present, is interpreted as a
 // JSON structure, with the keys mapping to preference names in the
 // "marionette." branch, and the values to the values of those prefs. So
 // something like {"enabled": true} would result in the marionette.enabled
 // pref being set to true, thus triggering marionette being enabled for
 // that startup.
-const ENV_PREF_VAR = "MOZ_MARIONETTE_PREF_STATE_ACROSS_RESTARTS";
+const ENV_PRESERVE_PREFS = "MOZ_MARIONETTE_PREF_STATE_ACROSS_RESTARTS";
 
 const ServerSocket = CC("@mozilla.org/network/server-socket;1",
     "nsIServerSocket",
     "initSpecialConnection");
 
 // Get preference value of |preferred|, falling back to |fallback|
 // if |preferred| is not user-modified and |fallback| exists.
 function getPref (preferred, fallback) {
@@ -107,18 +115,17 @@ const prefs = {
           Preferences.set("marionette." + prefName, prefs[prefName]);
         }
       }
     }
   },
 };
 
 function MarionetteComponent() {
-  // guards against this component
-  // being initialised multiple times
+  this.enabled = env.exists(ENV_ENABLED);
   this.running = false;
 
   // holds a reference to server.TCPListener
   this.server = null;
 
   // holds reference to ChromeWindow
   // used to run GFX sanity tests on Windows
   this.gfxWindow = null;
@@ -188,17 +195,17 @@ MarionetteComponent.prototype.observe = 
       }
       break;
 
     case "profile-after-change":
       // Using sessionstore-windows-restored as the xpcom category doesn't
       // seem to work, so we wait for that by adding an observer here.
       Services.obs.addObserver(this, "sessionstore-windows-restored");
 
-      prefs.readFromEnvironment(ENV_PREF_VAR);
+      prefs.readFromEnvironment(ENV_PRESERVE_PREFS);
 
       if (this.enabled) {
         // We want to suppress the modal dialog that's shown
         // when starting up in safe-mode to enable testing.
         if (Services.appinfo.inSafeMode) {
           Services.obs.addObserver(this, "domwindowopened");
         }
       }

--- a/testing/marionette/server.js
+++ b/testing/marionette/server.js
@@ -1,40 +1,49 @@
 /* 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/. */
 
 "use strict";
 
 const {Constructor: CC, classes: Cc, interfaces: Ci, utils: Cu} = Components;
 
-const loader = Cc["@mozilla.org/moz/jssubscript-loader;1"].getService(Ci.mozIJSSubScriptLoader);
-const ServerSocket = CC("@mozilla.org/network/server-socket;1", "nsIServerSocket", "initSpecialConnection");
+const loader = Cc["@mozilla.org/moz/jssubscript-loader;1"]
+    .getService(Ci.mozIJSSubScriptLoader);
+const ServerSocket = CC(
+    "@mozilla.org/network/server-socket;1",
+    "nsIServerSocket",
+    "initSpecialConnection");
 
 Cu.import("resource://gre/modules/Log.jsm");
 Cu.import("resource://gre/modules/Preferences.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/Task.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 Cu.import("chrome://marionette/content/assert.js");
 Cu.import("chrome://marionette/content/driver.js");
 Cu.import("chrome://marionette/content/error.js");
 Cu.import("chrome://marionette/content/message.js");
+Cu.import("chrome://marionette/content/transport.js");
 
-Cu.import("chrome://marionette/content/transport.js");
+XPCOMUtils.defineLazyServiceGetter(
+    this, "env", "@mozilla.org/process/environment;1", "nsIEnvironment");
 
 const logger = Log.repository.getLogger("Marionette");
 
 const {KeepWhenOffline, LoopbackOnly} = Ci.nsIServerSocket;
 
 this.EXPORTED_SYMBOLS = ["server"];
 this.server = {};
 
 const PROTOCOL_VERSION = 3;
 
+const ENV_ENABLED = "MOZ_MARIONETTE";
+
 const PREF_CONTENT_LISTENER = "marionette.contentListener";
 const PREF_PORT = "marionette.port";
 const PREF_RECOMMENDED = "marionette.prefs.recommended";
 
 // Marionette sets preferences recommended for automation when it starts,
 // unless |marionette.prefs.recommended| has been set to false.
 // Where noted, some prefs should also be set in the profile passed to
 // Marionette to prevent them from affecting startup, since some of these
@@ -328,16 +337,17 @@ server.TCPListener = class {
     const backlog = 1;
     this.socket = new ServerSocket(this.port, flags, backlog);
     this.socket.asyncListen(this);
     this.port = this.socket.port;
     Preferences.set(PREF_PORT, this.port);
 
     this.alive = true;
     this._acceptConnections = true;
+    env.set(ENV_ENABLED, "1");
   }
 
   stop () {
     if (!this.alive) {
       return;
     }
 
     this._acceptConnections = false;