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diff --git a/devtools/shared/loader/Loader.sys.mjs b/devtools/shared/loader/Loader.sys.mjs
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+++ b/devtools/shared/loader/Loader.sys.mjs
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+/* 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/. */
+
+/**
+ * Manages the base loader (base-loader.sys.mjs) instance used to load the developer tools.
+ */
+
+import {
+  Loader,
+  Require,
+  resolveURI,
+  unload,
+} from "resource://devtools/shared/loader/base-loader.sys.mjs";
+import { requireRawId } from "resource://devtools/shared/loader/loader-plugin-raw.sys.mjs";
+
+export const DEFAULT_SANDBOX_NAME = "DevTools (Module loader)";
+
+var gNextLoaderID = 0;
+
+/**
+ * The main devtools API. The standard instance of this loader is exported as
+ * |loader| below, but if a fresh copy of the loader is needed, then a new
+ * one can also be created.
+ *
+ * The two following boolean flags are used to control the sandboxes into
+ * which the modules are loaded.
+ * @param invisibleToDebugger boolean
+ *        If true, the modules won't be visible by the Debugger API.
+ *        This typically allows to hide server modules from the debugger panel.
+ * @param freshCompartment boolean
+ *        If true, the modules will be forced to be loaded in a distinct
+ *        compartment. It is typically used to load the modules in a distinct
+ *        system compartment, different from the main one, which is shared by
+ *        all JSMs, XPCOMs and modules loaded with this flag set to true.
+ *        We use this in order to debug modules loaded in this shared system
+ *        compartment. The debugger actor has to be running in a distinct
+ *        compartment than the context it is debugging.
+ * @param useDevToolsLoaderGlobal boolean
+ *        If true, the loader will reuse the current global to load other
+ *        modules instead of creating a sandbox with custom options. Cannot be
+ *        used with invisibleToDebugger and/or freshCompartment.
+ *        TODO: This should ultimately replace invisibleToDebugger.
+ */
+export function DevToolsLoader({
+  invisibleToDebugger = false,
+  freshCompartment = false,
+  useDevToolsLoaderGlobal = false,
+} = {}) {
+  if (useDevToolsLoaderGlobal && (invisibleToDebugger || freshCompartment)) {
+    throw new Error(
+      "Loader cannot use invisibleToDebugger or freshCompartment if useDevToolsLoaderGlobal is true"
+    );
+  }
+
+  const paths = {
+    // This resource:// URI is only registered when running DAMP tests.
+    // This is done by: testing/talos/talos/tests/devtools/addon/api.js
+    "damp-test": "resource://damp-test/content",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    devtools: "resource://devtools",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    // Allow access to xpcshell test items from the loader.
+    "xpcshell-test": "resource://test",
+
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    // Allow access to locale data using paths closer to what is
+    // used in the source tree.
+    "devtools/client/locales": "chrome://devtools/locale",
+    "devtools/shared/locales": "chrome://devtools-shared/locale",
+    "devtools/startup/locales": "chrome://devtools-startup/locale",
+    "toolkit/locales": "chrome://global/locale",
+  };
+
+  const sharedGlobal = useDevToolsLoaderGlobal
+    ? Cu.getGlobalForObject({})
+    : undefined;
+  this.loader = new Loader({
+    paths,
+    sharedGlobal,
+    invisibleToDebugger,
+    freshCompartment,
+    sandboxName: useDevToolsLoaderGlobal
+      ? "DevTools (Server Module Loader)"
+      : DEFAULT_SANDBOX_NAME,
+    // Make sure `define` function exists. JSON Viewer needs modules in AMD
+    // format, as it currently uses RequireJS from a content document and
+    // can't access our usual loaders. So, any modules shared with the JSON
+    // Viewer should include a define wrapper:
+    //
+    //   // Make this available to both AMD and CJS environments
+    //   define(function(require, exports, module) {
+    //     ... code ...
+    //   });
+    //
+    // Bug 1248830 will work out a better plan here for our content module
+    // loading needs, especially as we head towards devtools.html.
+    supportAMDModules: true,
+    requireHook: (id, require) => {
+      if (id.startsWith("raw!") || id.startsWith("theme-loader!")) {
+        return requireRawId(id, require);
+      }
+      return require(id);
+    },
+  });
+
+  this.require = Require(this.loader, { id: "devtools" });
+
+  // Various globals are available from ESM, but not from sandboxes,
+  // inject them into the globals list.
+  // Changes here should be mirrored to devtools/.eslintrc.
+  const injectedGlobals = {
+    CanonicalBrowsingContext,
+    console,
+    BrowsingContext,
+    ChromeWorker,
+    DebuggerNotificationObserver,
+    DOMPoint,
+    DOMQuad,
+    DOMRect,
+    fetch,
+    HeapSnapshot,
+    IOUtils,
+    L10nRegistry,
+    Localization,
+    NamedNodeMap,
+    NodeFilter,
+    PathUtils,
+    Services,
+    StructuredCloneHolder,
+    TelemetryStopwatch,
+    WebExtensionPolicy,
+    WindowGlobalParent,
+    WindowGlobalChild,
+  };
+  for (const name in injectedGlobals) {
+    this.loader.globals[name] = injectedGlobals[name];
+  }
+
+  // Fetch custom pseudo modules and globals
+  const { modules, globals } = this.require(
+    "resource://devtools/shared/loader/builtin-modules.js"
+  );
+
+  // Register custom pseudo modules to the current loader instance
+  for (const id in modules) {
+    const uri = resolveURI(id, this.loader.mapping);
+    this.loader.modules[uri] = {
+      get exports() {
+        return modules[id];
+      },
+    };
+  }
+
+  // Register custom globals to the current loader instance
+  Object.defineProperties(
+    this.loader.sharedGlobal,
+    Object.getOwnPropertyDescriptors(globals)
+  );
+
+  // Define the loader id for these two usecases:
+  // * access via the JSM (this.id)
+  // let { loader } = ChromeUtils.importESModule("resource://devtools/shared/loader/Loader.sys.mjs");
+  // loader.id
+  this.id = gNextLoaderID++;
+  // * access via module's `loader` global
+  // loader.id
+  globals.loader.id = this.id;
+  globals.loader.invisibleToDebugger = invisibleToDebugger;
+
+  // Expose lazy helpers on `loader`
+  // ie. when you use it like that from a JSM:
+  // let { loader } = ChromeUtils.importESModule("resource://devtools/shared/loader/Loader.sys.mjs");
+  // loader.lazyGetter(...);
+  this.lazyGetter = globals.loader.lazyGetter;
+  this.lazyServiceGetter = globals.loader.lazyServiceGetter;
+  this.lazyRequireGetter = globals.loader.lazyRequireGetter;
+}
+
+DevToolsLoader.prototype = {
+  destroy(reason = "shutdown") {
+    unload(this.loader, reason);
+    delete this.loader;
+  },
+
+  /**
+   * Return true if |id| refers to something requiring help from a
+   * loader plugin.
+   */
+  isLoaderPluginId(id) {
+    return id.startsWith("raw!");
+  },
+};
+
+// Export the standard instance of DevToolsLoader used by the tools.
+export var loader = new DevToolsLoader({
+  /**
+   * Sets whether the compartments loaded by this instance should be invisible
+   * to the debugger.  Invisibility is needed for loaders that support debugging
+   * of chrome code.  This is true of remote target environments, like Fennec or
+   * B2G.  It is not the default case for desktop Firefox because we offer the
+   * Browser Toolbox for chrome debugging there, which uses its own, separate
+   * loader instance.
+   * @see devtools/client/framework/browser-toolbox/Launcher.sys.mjs
+   */
+  invisibleToDebugger: Services.appinfo.name !== "Firefox",
+});
+
+export var require = loader.require;