--- a/testing/marionette/addon.js
+++ b/testing/marionette/addon.js
@@ -1,93 +1,104 @@
 /* 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 {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+const {interfaces: Ci, utils: Cu} = Components;
 
 Cu.import("resource://gre/modules/AddonManager.jsm");
 Cu.import("resource://gre/modules/FileUtils.jsm");
 
 Cu.import("chrome://marionette/content/error.js");
 
 this.EXPORTED_SYMBOLS = ["addon"];
 
 this.addon = {};
 
+// from https://developer.mozilla.org/en-US/Add-ons/Add-on_Manager/AddonManager#AddonInstall_errors
+addon.Errors = {
+  [-1]: "ERROR_NETWORK_FAILURE: A network error occured.",
+  [-2]: "ERROR_INCORECT_HASH: The downloaded file did not match the expected hash.",
+  [-3]: "ERROR_CORRUPT_FILE: The file appears to be corrupt.",
+  [-4]: "ERROR_FILE_ACCESS: There was an error accessing the filesystem.",
+  [-5]: "ERROR_SIGNEDSTATE_REQUIRED: The addon must be signed and isn't.",
+};
+
+function lookupError(code) {
+  let msg = addon.Errors[code];
+  return new UnknownError(msg);
+}
+
 /**
- * Installs Firefox addon.
+ * Install a Firefox addon.
  *
- * If the addon is restartless, it can be used right away. Otherwise a
- * restart is needed.
+ * If the addon is restartless, it can be used right away.  Otherwise a
+ * restart is required.
  *
- * Temporary addons will automatically be unisntalled on shutdown and
+ * Temporary addons will automatically be uninstalled on shutdown and
  * do not need to be signed, though they must be restartless.
  *
  * @param {string} path
- *     Full path to the extension package archive to be installed.
+ *     Full path to the extension package archive.
  * @param {boolean=} temporary
- *     Install the add-on temporarily if true.
+ *     True to install the addon temporarily, false (default) otherwise.
  *
- * @return {Promise.<string>}
- *     Addon ID string of the newly installed addon.
+ * @return {Promise: string}
+ *     Addon ID.
  *
- * @throws {AddonError}
- *     if installation fails
+ * @throws {UnknownError}
+ *     If there is a problem installing the addon.
  */
 addon.install = function(path, temporary = false) {
   return new Promise((resolve, reject) => {
+    let file = new FileUtils.File(path);
+
     let listener = {
       onInstallEnded: function(install, addon) {
         resolve(addon.id);
       },
 
       onInstallFailed: function(install) {
-        reject(new AddonError(install.error));
+        reject(lookupError(install.error));
       },
 
       onInstalled: function(addon) {
         AddonManager.removeAddonListener(listener);
         resolve(addon.id);
       }
     };
 
-    let file = new FileUtils.File(path);
-
-    // temporary addons
-    if (temp) {
-      AddonManager.addAddonListener(listener);
-      AddonManager.installTemporaryAddon(file);
-    }
-
-    // addons that require restart
-    else {
+    if (!temporary) {
       AddonManager.getInstallForFile(file, function(aInstall) {
-        if (aInstall.error != 0) {
-          reject(new AddonError(aInstall.error));
+        if (aInstall.error !== 0) {
+          reject(lookupError(aInstall.error));
         }
         aInstall.addListener(listener);
         aInstall.install();
       });
+    } else {
+      AddonManager.addAddonListener(listener);
+      AddonManager.installTemporaryAddon(file);
     }
   });
 };
 
 /**
  * Uninstall a Firefox addon.
  *
- * If the addon is restartless, it will be uninstalled right
- * away. Otherwise a restart is necessary.
+ * If the addon is restartless it will be uninstalled right away.
+ * Otherwise, Firefox must be restarted for the change to take effect.
  *
  * @param {string} id
- *     Addon ID to uninstall.
+ *     ID of the addon to uninstall.
  *
  * @return {Promise}
  */
 addon.uninstall = function(id) {
   return new Promise(resolve => {
-    AddonManager.getAddonByID(arguments[0], function(addon) {
+    AddonManager.getAddonByID(id, function(addon) {
       addon.uninstall();
+      resolve();
     });
   });
 };

--- a/testing/marionette/client/marionette_driver/addons.py
+++ b/testing/marionette/client/marionette_driver/addons.py
@@ -1,120 +1,70 @@
 # 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/.
 
-from .errors import MarionetteException
+from . import errors
 
-__all__ = ['Addons', 'AddonInstallException']
+__all__ = ["Addons", "AddonInstallException"]
 
 
-# From https://developer.mozilla.org/en-US/Add-ons/Add-on_Manager/AddonManager#AddonInstall_errors
-ADDON_INSTALL_ERRORS = {
-    -1: "ERROR_NETWORK_FAILURE: A network error occured.",
-    -2: "ERROR_INCORECT_HASH: The downloaded file did not match the expected hash.",
-    -3: "ERROR_CORRUPT_FILE: The file appears to be corrupt.",
-    -4: "ERROR_FILE_ACCESS: There was an error accessing the filesystem.",
-    -5: "ERROR_SIGNEDSTATE_REQUIRED: The addon must be signed and isn't.",
-}
-
-
-class AddonInstallException(MarionetteException):
+class AddonInstallException(errors.MarionetteException):
     pass
 
 
 class Addons(object):
-    """
-    An API for installing and inspecting addons during Gecko runtime. This
-    is a partially implemented wrapper around Gecko's `AddonManager API`_.
+    """An API for installing and inspecting addons during Gecko
+    runtime. This is a partially implemented wrapper around Gecko's
+    `AddonManager API`_.
 
     For example::
 
         from marionette_driver.addons import Addons
         addons = Addons(marionette)
-        addons.install('path/to/extension.xpi')
+        addons.install("/path/to/extension.xpi")
 
     .. _AddonManager API: https://developer.mozilla.org/en-US/Add-ons/Add-on_Manager
+
     """
-
     def __init__(self, marionette):
         self._mn = marionette
 
     def install(self, path, temp=False):
-        """Install an addon.
+        """Install a Firefox addon.
 
         If the addon is restartless, it can be used right away. Otherwise
         a restart using :func:`~marionette_driver.marionette.Marionette.restart`
         will be needed.
 
         :param path: A file path to the extension to be installed.
         :param temp: Install a temporary addon. Temporary addons will
                      automatically be uninstalled on shutdown and do not need
                      to be signed, though they must be restartless.
+
         :returns: The addon ID string of the newly installed addon.
+
         :raises: :exc:`AddonInstallException`
-        """
-        with self._mn.using_context('chrome'):
-            addon_id, status = self._mn.execute_async_script("""
-              let fileUtils = Components.utils.import("resource://gre/modules/FileUtils.jsm");
-              let FileUtils = fileUtils.FileUtils;
-              Components.utils.import("resource://gre/modules/AddonManager.jsm");
-              let listener = {
-                onInstallEnded: function(install, addon) {
-                  marionetteScriptFinished([addon.id, 0]);
-                },
-
-                onInstallFailed: function(install) {
-                  marionetteScriptFinished([null, install.error]);
-                },
-
-                onInstalled: function(addon) {
-                  AddonManager.removeAddonListener(listener);
-                  marionetteScriptFinished([addon.id, 0]);
-                }
-              }
 
-              let file = new FileUtils.File(arguments[0]);
-              let temp = arguments[1];
-
-              if (!temp) {
-                AddonManager.getInstallForFile(file, function(aInstall) {
-                  if (aInstall.error != 0) {
-                    marionetteScriptFinished([null, aInstall.error]);
-                  }
-                  aInstall.addListener(listener);
-                  aInstall.install();
-                });
-              } else {
-                AddonManager.addAddonListener(listener);
-                AddonManager.installTemporaryAddon(file);
-              }
-            """, script_args=[path, temp], debug_script=True)
-
-        if status:
-            if status in ADDON_INSTALL_ERRORS:
-                raise AddonInstallException(ADDON_INSTALL_ERRORS[status])
-            raise AddonInstallException(
-                "Addon failed to install with return code: {}".format(status))
-        return addon_id
+        """
+        body = {"path": path, "temporary": temp}
+        try:
+            return self._mn._send_message("addon:install", body, key="value")
+        except errors.UnknownException as e:
+            raise AddonInstallException(e)
 
     def uninstall(self, addon_id):
-        """Uninstall an addon.
+        """Uninstall a Firefox addon.
 
         If the addon is restartless, it will be uninstalled right away.
         Otherwise a restart using :func:`~marionette_driver.marionette.Marionette.restart`
         will be needed.
 
         If the call to uninstall is resulting in a `ScriptTimeoutException`,
         an invalid ID is likely being passed in. Unfortunately due to
         AddonManager's implementation, it's hard to retrieve this error from
         Python.
 
         :param addon_id: The addon ID string to uninstall.
+
         """
-        with self._mn.using_context('chrome'):
-            return self._mn.execute_async_script("""
-              Components.utils.import("resource://gre/modules/AddonManager.jsm");
-              AddonManager.getAddonByID(arguments[0], function(addon) {
-                addon.uninstall();
-                marionetteScriptFinished(0);
-              });
-            """, script_args=[addon_id])
+        body = {"id": addon_id}
+        self._mn._send_message("addon:uninstall", body)

--- a/testing/marionette/driver.js
+++ b/testing/marionette/driver.js
@@ -13,16 +13,18 @@ Cu.import("resource://gre/modules/Log.js
 Cu.import("resource://gre/modules/Preferences.jsm");
 Cu.import("resource://gre/modules/Services.jsm");
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 XPCOMUtils.defineLazyServiceGetter(
     this, "cookieManager", "@mozilla.org/cookiemanager;1", "nsICookieManager2");
 
 Cu.import("chrome://marionette/content/accessibility.js");
+Cu.import("chrome://marionette/content/action.js");
+Cu.import("chrome://marionette/content/addon.js");
 Cu.import("chrome://marionette/content/assert.js");
 Cu.import("chrome://marionette/content/atom.js");
 Cu.import("chrome://marionette/content/browser.js");
 Cu.import("chrome://marionette/content/element.js");
 Cu.import("chrome://marionette/content/error.js");
 Cu.import("chrome://marionette/content/evaluate.js");
 Cu.import("chrome://marionette/content/event.js");
 Cu.import("chrome://marionette/content/interaction.js");
@@ -2600,16 +2602,44 @@ GeckoDriver.prototype.quitApplication = 
 
   this._server.acceptConnections = false;
   resp.send();
 
   this.sessionTearDown();
   Services.startup.quit(flags);
 };
 
+GeckoDriver.prototype.installAddon = function(cmd, resp) {
+  if (this.appName != "Firefox") {
+    throw new UnsupportedOperationError();
+  }
+
+  let path = cmd.parameters.path;
+  let temp = cmd.parameters.temporary || false;
+  if (typeof path == "undefined" || typeof path != "string" ||
+      typeof temp != "boolean") {
+    throw InvalidArgumentError();
+  }
+
+  return addon.install(path, temp);
+};
+
+GeckoDriver.prototype.uninstallAddon = function(cmd, resp) {
+  if (this.appName != "Firefox") {
+    throw new UnsupportedOperationError();
+  }
+
+  let id = cmd.parameters.id;
+  if (typeof id == "undefined" || typeof id != "string") {
+    throw new InvalidArgumentError();
+  }
+
+  return addon.uninstall(id);
+};
+
 /**
  * Helper function to convert an outerWindowID into a UID that Marionette
  * tracks.
  */
 GeckoDriver.prototype.generateFrameId = function(id) {
   let uid = id + (this.appName == "B2G" ? "-b2g" : "");
   return uid;
 };
@@ -2855,9 +2885,12 @@ GeckoDriver.prototype.commands = {
   "acceptDialog": GeckoDriver.prototype.acceptDialog,
   "getTextFromDialog": GeckoDriver.prototype.getTextFromDialog,
   "sendKeysToDialog": GeckoDriver.prototype.sendKeysToDialog,
   "acceptConnections": GeckoDriver.prototype.acceptConnections,
   "quitApplication": GeckoDriver.prototype.quitApplication,
 
   "localization:l10n:localizeEntity": GeckoDriver.prototype.localizeEntity,
   "localization:l10n:localizeProperty": GeckoDriver.prototype.localizeProperty,
+
+  "addon:install": GeckoDriver.prototype.installAddon,
+  "addon:uninstall": GeckoDriver.prototype.uninstallAddon,
 };

--- a/testing/marionette/jar.mn
+++ b/testing/marionette/jar.mn
@@ -24,16 +24,17 @@ marionette.jar:
   content/capture.js (capture.js)
   content/cookies.js (cookies.js)
   content/atom.js (atom.js)
   content/evaluate.js (evaluate.js)
   content/logging.js (logging.js)
   content/navigate.js (navigate.js)
   content/l10n.js (l10n.js)
   content/assert.js (assert.js)
+  content/addon.js (addon.js)
 #ifdef ENABLE_TESTS
   content/test.xul  (harness/marionette/chrome/test.xul)
   content/test2.xul  (harness/marionette/chrome/test2.xul)
   content/test_dialog.xul  (harness/marionette/chrome/test_dialog.xul)
   content/test_nested_iframe.xul  (harness/marionette/chrome/test_nested_iframe.xul)
   content/test_anonymous_content.xul  (harness/marionette/chrome/test_anonymous_content.xul)
 #endif