--- a/testing/marionette/server.js
+++ b/testing/marionette/server.js
@@ -22,16 +22,238 @@ Cu.import("chrome://marionette/content/s
 loader.loadSubScript("resource://devtools/shared/transport/transport.js");
 
 const logger = Log.repository.getLogger("Marionette");
 
 this.EXPORTED_SYMBOLS = ["MarionetteServer"];
 
 const CONTENT_LISTENER_PREF = "marionette.contentListener";
 
+// 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
+// are checked before Marionette initialises.
+const RECOMMENDED_PREFS = new Map([
+
+  // Disable automatic downloading of new releases.
+  //
+  // This should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["app.update.auto", false],
+
+  // Disable automatically upgrading Firefox.
+  //
+  // This should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["app.update.enabled", false],
+
+  // Increase the APZ content response timeout in tests to 1 minute.
+  // This is to accommodate the fact that test environments tends to be
+  // slower than production environments (with the b2g emulator being
+  // the slowest of them all), resulting in the production timeout value
+  // sometimes being exceeded and causing false-positive test failures.
+  //
+  // (bug 1176798, bug 1177018, bug 1210465)
+  ["apz.content_response_timeout", 60000],
+
+  // Indicate that the download panel has been shown once so that
+  // whichever download test runs first doesn't show the popup
+  // inconsistently.
+  ["browser.download.panel.shown", true],
+
+  // Do not show the EULA notification.
+  //
+  // This should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["browser.EULA.override", true],
+
+  // Turn off about:newtab and make use of about:blank instead for new
+  // opened tabs.
+  //
+  // This should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["browser.newtabpage.enabled", false],
+
+  // Assume the about:newtab page's intro panels have been shown to not
+  // depend on which test runs first and happens to open about:newtab
+  ["browser.newtabpage.introShown", true],
+
+  // Never start the browser in offline mode
+  //
+  // This should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["browser.offline", false],
+
+  // Background thumbnails in particular cause grief, and disabling
+  // thumbnails in general cannot hurt
+  ["browser.pagethumbnails.capturing_disabled", true],
+
+  // Avoid performing Reader Mode intros during tests
+  ["browser.reader.detectedFirstArticle", true],
+
+  // Disable safebrowsing components.
+  //
+  // These should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["browser.safebrowsing.blockedURIs.enabled", false],
+  ["browser.safebrowsing.downloads.enabled", false],
+  ["browser.safebrowsing.enabled", false],
+  ["browser.safebrowsing.forbiddenURIs.enabled", false],
+  ["browser.safebrowsing.malware.enabled", false],
+  ["browser.safebrowsing.phishing.enabled", false],
+
+  // Disable updates to search engines.
+  //
+  // Should be set in profile.
+  ["browser.search.update", false],
+
+  // Do not restore the last open set of tabs if the browser has crashed
+  ["browser.sessionstore.resume_from_crash", false],
+
+  // Don't check for the default web browser during startup.
+  //
+  // These should also be set in the profile prior to starting Firefox,
+  // as it is picked up at runtime.
+  ["browser.shell.checkDefaultBrowser", false],
+
+  // Start with a blank page (about:blank)
+  ["browser.startup.page", 0],
+
+  // Disable tab animation
+  ["browser.tabs.animate", false],
+
+  // Do not allow background tabs to be zombified, otherwise for tests
+  // that open additional tabs, the test harness tab itself might get
+  // unloaded
+  ["browser.tabs.disableBackgroundZombification", false],
+
+  // Do not warn when closing all other open tabs
+  ["browser.tabs.warnOnCloseOtherTabs", false],
+
+  // Do not warn when multiple tabs will be opened
+  ["browser.tabs.warnOnOpen", false],
+
+  // Disable first run splash page on Windows 10
+  ["browser.usedOnWindows10.introURL", ""],
+
+  // Disable the UI tour.
+  //
+  // Should be set in profile.
+  ["browser.uitour.enabled", false],
+
+  // Do not show datareporting policy notifications which can
+  // interfere with tests
+  ["datareporting.healthreport.about.reportUrl", "http://%(server)s/dummy/abouthealthreport/"],
+  ["datareporting.healthreport.documentServerURI", "http://%(server)s/dummy/healthreport/"],
+  ["datareporting.healthreport.logging.consoleEnabled", false],
+  ["datareporting.healthreport.service.enabled", false],
+  ["datareporting.healthreport.service.firstRun", false],
+  ["datareporting.healthreport.uploadEnabled", false],
+  ["datareporting.policy.dataSubmissionEnabled", false],
+  ["datareporting.policy.dataSubmissionPolicyAccepted", false],
+  ["datareporting.policy.dataSubmissionPolicyBypassNotification", true],
+
+  // Disable popup-blocker
+  ["dom.disable_open_during_load", false],
+
+  // Disable the ProcessHangMonitor
+  ["dom.ipc.reportProcessHangs", false],
+
+  // Disable slow script dialogues
+  ["dom.max_chrome_script_run_time", 0],
+  ["dom.max_script_run_time", 0],
+
+  // Only load extensions from the application and user profile
+  // AddonManager.SCOPE_PROFILE + AddonManager.SCOPE_APPLICATION
+  //
+  // Should be set in profile.
+  ["extensions.autoDisableScopes", 0],
+  ["extensions.enabledScopes", 5],
+
+  // Do not block add-ons for e10s
+  ["extensions.e10sBlocksEnabling", false],
+
+  // Disable metadata caching for installed add-ons by default
+  ["extensions.getAddons.cache.enabled", false],
+
+  // Disable intalling any distribution extensions or add-ons.
+  // Should be set in profile.
+  ["extensions.installDistroAddons", false],
+  ["extensions.showMismatchUI", false],
+
+  // Turn off extension updates so they do not bother tests
+  ["extensions.update.enabled", false],
+  ["extensions.update.notifyUser", false],
+
+  // Make sure opening about:addons will not hit the network
+  ["extensions.webservice.discoverURL", "http://%(server)s/dummy/discoveryURL"],
+
+  // Allow the application to have focus even it runs in the background
+  ["focusmanager.testmode", true],
+
+  // Disable useragent updates
+  ["general.useragent.updates.enabled", false],
+
+  // Always use network provider for geolocation tests so we bypass the
+  // macOS dialog raised by the corelocation provider
+  ["geo.provider.testing", true],
+
+  // Do not scan Wifi
+  ["geo.wifi.scan", false],
+
+  // No hang monitor
+  ["hangmonitor.timeout", 0],
+
+  // Show chrome errors and warnings in the error console
+  ["javascript.options.showInConsole", true],
+
+  // Make sure the disk cache doesn't get auto disabled
+  ["network.http.bypass-cachelock-threshold", 200000],
+
+  // Do not prompt for temporary redirects
+  ["network.http.prompt-temp-redirect", false],
+
+  // Disable speculative connections so they are not reported as leaking
+  // when they are hanging around
+  ["network.http.speculative-parallel-limit", 0],
+
+  // Do not automatically switch between offline and online
+  ["network.manage-offline-status", false],
+
+  // Make sure SNTP requests do not hit the network
+  ["network.sntp.pools", "%(server)s"],
+
+  // Local documents have access to all other local documents,
+  // including directory listings
+  ["security.fileuri.strict_origin_policy", false],
+
+  // Tests do not wait for the notification button security delay
+  ["security.notification_enable_delay", 0],
+
+  // Ensure blocklist updates do not hit the network
+  ["services.settings.server", "http://%(server)s/dummy/blocklist/"],
+
+  // Do not automatically fill sign-in forms with known usernames and
+  // passwords
+  ["signon.autofillForms", false],
+
+  // Disable password capture, so that tests that include forms are not
+  // influenced by the presence of the persistent doorhanger notification
+  ["signon.rememberSignons", false],
+
+  // Disable first-run welcome page
+  ["startup.homepage_welcome_url", "about:blank"],
+  ["startup.homepage_welcome_url.additional", ""],
+
+  // Prevent starting into safe mode after application crashes
+  ["toolkit.startup.max_resumed_crashes", -1],
+
+]);
+
 /**
  * Bootstraps Marionette and handles incoming client connections.
  *
  * Once started, it opens a TCP socket sporting the debugger transport
  * protocol on the provided port.  For every new client a Dispatcher is
  * created.
  *
  * @param {number} port
@@ -42,16 +264,17 @@ const CONTENT_LISTENER_PREF = "marionett
  */
 this.MarionetteServer = function (port, forceLocal) {
   this.port = port;
   this.forceLocal = forceLocal;
   this.conns = {};
   this.nextConnId = 0;
   this.alive = false;
   this._acceptConnections = false;
+  this.alteredPrefs = new Set();
 };
 
 /**
  * Function produces a GeckoDriver.
  *
  * Determines application nameto initialise the driver with.
  *
  * @return {GeckoDriver}
@@ -71,31 +294,49 @@ MarionetteServer.prototype.__defineSette
 
   this._acceptConnections = value;
 });
 
 MarionetteServer.prototype.start = function() {
   if (this.alive) {
     return;
   }
+
+  // set recommended preferences if they are not already user-defined
+  for (let [k, v] of RECOMMENDED_PREFS) {
+    if (!Preferences.isSet(k)) {
+      logger.debug(`Setting recommended pref ${k} to ${v}`);
+      Preferences.set(k, v);
+      this.alteredPrefs.add(k);
+    }
+  }
+
   let flags = Ci.nsIServerSocket.KeepWhenOffline;
   if (this.forceLocal) {
     flags |= Ci.nsIServerSocket.LoopbackOnly;
   }
   this.listener = new ServerSocket(this.port, flags, 1);
   this.listener.asyncListen(this);
+
   this.alive = true;
   this._acceptConnections = true;
 };
 
 MarionetteServer.prototype.stop = function() {
   if (!this.alive) {
     return;
   }
+
+  for (let k of this.alteredPrefs) {
+    logger.debug(`Resetting recommended pref ${k}`);
+    Preferences.reset(k);
+  }
   this.closeListener();
+
+  this.alteredPrefs.clear();
   this.alive = false;
   this._acceptConnections = false;
 };
 
 MarionetteServer.prototype.closeListener = function() {
   this.listener.close();
   this.listener = null;
 };
@@ -121,9 +362,8 @@ MarionetteServer.prototype.onSocketAccep
   transport.ready();
 };
 
 MarionetteServer.prototype.onConnectionClosed = function (conn) {
   let id = conn.connId;
   delete this.conns[id];
   logger.debug(`Closed connection ${id}`);
 };
-