--- a/toolkit/devtools/Loader.jsm
+++ b/toolkit/devtools/Loader.jsm
@@ -311,20 +311,35 @@ DevToolsLoader.prototype = {
    *    The property name.
    * @param String module
    *    The module path.
    * @param Boolean destructure
    *    Pass true if the property name is a member of the module's exports.
    */
   lazyRequireGetter: function (obj, property, module, destructure) {
     Object.defineProperty(obj, property, {
-      get: () => destructure
-        ? this.require(module)[property]
-        : this.require(module || property),
-      configurable: true
+      get: () => {
+        // Redefine this accessor property as a data property.
+        // Delete it first, to rule out "too much recursion" in case obj is
+        // a proxy whose defineProperty handler might unwittingly trigger this
+        // getter again.
+        delete obj[property];
+        let value = destructure
+          ? this.require(module)[property]
+          : this.require(module || property);
+        Object.defineProperty(obj, property, {
+          value,
+          writable: true,
+          configurable: true,
+          enumerable: true
+        });
+        return value;
+      },
+      configurable: true,
+      enumerable: true
     });
   },
 
   /**
    * Add a URI to the loader.
    * @param string id
    *    The module id that can be used within the loader to refer to this module.
    * @param string uri

--- a/toolkit/devtools/server/actors/utils/TabSources.js
+++ b/toolkit/devtools/server/actors/utils/TabSources.js
@@ -1,15 +1,21 @@
-const Services = require("Services");
+/* 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 { Ci, Cu } = require("chrome");
+const Services = require("Services");
 const DevToolsUtils = require("devtools/toolkit/DevToolsUtils");
+const { dbg_assert, fetch } = DevToolsUtils;
 const EventEmitter = require("devtools/toolkit/event-emitter");
-const { dbg_assert, fetch } = require("devtools/toolkit/DevToolsUtils");
 const { OriginalLocation, GeneratedLocation, getOffsetColumn } = require("devtools/server/actors/common");
-const { resolve } = require("promise");
+const { resolve } = Promise;
 
 loader.lazyRequireGetter(this, "SourceActor", "devtools/server/actors/script", true);
 loader.lazyRequireGetter(this, "isEvalSource", "devtools/server/actors/script", true);
 loader.lazyRequireGetter(this, "SourceMapConsumer", "source-map", true);
 loader.lazyRequireGetter(this, "SourceMapGenerator", "source-map", true);
 
 /**
  * Manages the sources for a thread. Handles source maps, locations in the

--- a/toolkit/devtools/server/actors/webbrowser.js
+++ b/toolkit/devtools/server/actors/webbrowser.js
@@ -3,24 +3,24 @@
 /* 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";
 
 let { Ci, Cu } = require("chrome");
 let Services = require("Services");
+let promise = require("promise");
 let { ActorPool, createExtraActors, appendExtraActors } = require("devtools/server/actors/common");
 let { DebuggerServer } = require("devtools/server/main");
 let DevToolsUtils = require("devtools/toolkit/DevToolsUtils");
 let { dbg_assert } = DevToolsUtils;
 let { TabSources, isHiddenSource } = require("./utils/TabSources");
 let makeDebugger = require("./utils/make-debugger");
 
-let {Promise: promise} = Cu.import("resource://gre/modules/Promise.jsm", {});
 Cu.import("resource://gre/modules/XPCOMUtils.jsm");
 
 loader.lazyRequireGetter(this, "RootActor", "devtools/server/actors/root", true);
 loader.lazyRequireGetter(this, "AddonThreadActor", "devtools/server/actors/script", true);
 loader.lazyRequireGetter(this, "ThreadActor", "devtools/server/actors/script", true);
 loader.lazyRequireGetter(this, "mapURIToAddonID", "devtools/server/actors/utils/map-uri-to-addon-id");
 loader.lazyImporter(this, "AddonManager", "resource://gre/modules/AddonManager.jsm");