diff --git a/devtools/client/definitions.js b/devtools/client/definitions.js
index 6c0796095c73..fc85bf43965f 100644
--- a/devtools/client/definitions.js
+++ b/devtools/client/definitions.js
@@ -12,6 +12,7 @@ loader.lazyGetter(this, "OptionsPanel", () => require("devtools/client/framework
 loader.lazyGetter(this, "InspectorPanel", () => require("devtools/client/inspector/panel").InspectorPanel);
 loader.lazyGetter(this, "WebConsolePanel", () => require("devtools/client/webconsole/panel").WebConsolePanel);
 loader.lazyGetter(this, "DebuggerPanel", () => require("devtools/client/debugger/panel").DebuggerPanel);
+loader.lazyGetter(this, "NewDebuggerPanel", () => require("devtools/client/debugger/new/panel").DebuggerPanel);
 loader.lazyGetter(this, "StyleEditorPanel", () => require("devtools/client/styleeditor/styleeditor-panel").StyleEditorPanel);
 loader.lazyGetter(this, "ShaderEditorPanel", () => require("devtools/client/shadereditor/panel").ShaderEditorPanel);
 loader.lazyGetter(this, "CanvasDebuggerPanel", () => require("devtools/client/canvasdebugger/panel").CanvasDebuggerPanel);
@@ -155,8 +156,6 @@ Tools.jsdebugger = {
 
 function switchDebugger() {
   if (Services.prefs.getBoolPref("devtools.debugger.new-debugger-frontend")) {
-    const NewDebuggerPanel = require("devtools/client/debugger/new/panel").DebuggerPanel;
-
     Tools.jsdebugger.url = "chrome://devtools/content/debugger/new/index.html";
     Tools.jsdebugger.build = function (iframeWindow, toolbox) {
       return new NewDebuggerPanel(iframeWindow, toolbox);
diff --git a/devtools/client/framework/devtools-browser.js b/devtools/client/framework/devtools-browser.js
index 385adc131b23..0fdc6f33c125 100644
--- a/devtools/client/framework/devtools-browser.js
+++ b/devtools/client/framework/devtools-browser.js
@@ -18,7 +18,6 @@ const promise = require("promise");
 const defer = require("devtools/shared/defer");
 const Telemetry = require("devtools/client/shared/telemetry");
 const { gDevTools } = require("./devtools");
-const { when: unload } = require("sdk/system/unload");
 
 // Load target and toolbox lazily as they need gDevTools to be fully initialized
 loader.lazyRequireGetter(this, "TargetFactory", "devtools/client/framework/target", true);
@@ -142,6 +141,16 @@ var gDevToolsBrowser = exports.gDevToolsBrowser = {
           }
         }
         break;
+      case "quit-application":
+        gDevToolsBrowser.destroy({ shuttingDown: true });
+        break;
+      case "sdk:loader:destroy":
+        // This event is fired when the devtools loader unloads, which happens
+        // only when the add-on workflow ask devtools to be reloaded.
+        if (subject.wrappedJSObject == require('@loader/unload')) {
+          gDevToolsBrowser.destroy({ shuttingDown: false });
+        }
+        break;
     }
   },
 
@@ -730,12 +739,19 @@ var gDevToolsBrowser = exports.gDevToolsBrowser = {
   },
 
   /**
-   * All browser windows have been closed, tidy up remaining objects.
+   * Either the SDK Loader has been destroyed by the add-on contribution
+   * workflow, or firefox is shutting down.
+
+   * @param {boolean} shuttingDown
+   *        True if firefox is currently shutting down. We may prevent doing
+   *        some cleanups to speed it up. Otherwise everything need to be
+   *        cleaned up in order to be able to load devtools again.
    */
-  destroy: function () {
+  destroy: function ({ shuttingDown }) {
     Services.prefs.removeObserver("devtools.", gDevToolsBrowser);
     Services.obs.removeObserver(gDevToolsBrowser, "browser-delayed-startup-finished");
-    Services.obs.removeObserver(gDevToolsBrowser.destroy, "quit-application");
+    Services.obs.removeObserver(gDevToolsBrowser, "quit-application");
+    Services.obs.removeObserver(gDevToolsBrowser, "sdk:loader:destroy");
 
     gDevToolsBrowser._pingTelemetry();
     gDevToolsBrowser._telemetry = null;
@@ -743,6 +759,8 @@ var gDevToolsBrowser = exports.gDevToolsBrowser = {
     for (let win of gDevToolsBrowser._trackedBrowserWindows) {
       gDevToolsBrowser._forgetBrowserWindow(win);
     }
+
+    gDevTools.destroy({ shuttingDown });
   },
 };
 
@@ -766,8 +784,10 @@ gDevTools.on("tool-unregistered", function (ev, toolId) {
 gDevTools.on("toolbox-ready", gDevToolsBrowser._updateMenuCheckbox);
 gDevTools.on("toolbox-destroyed", gDevToolsBrowser._updateMenuCheckbox);
 
-Services.obs.addObserver(gDevToolsBrowser.destroy, "quit-application", false);
+Services.obs.addObserver(gDevToolsBrowser, "quit-application", false);
 Services.obs.addObserver(gDevToolsBrowser, "browser-delayed-startup-finished", false);
+// Watch for module loader unload. Fires when the tools are reloaded.
+Services.obs.addObserver(gDevToolsBrowser, "sdk:loader:destroy", false);
 
 // Fake end of browser window load event for all already opened windows
 // that is already fully loaded.
@@ -778,8 +798,3 @@ while (enumerator.hasMoreElements()) {
     gDevToolsBrowser._registerBrowserWindow(win);
   }
 }
-
-// Watch for module loader unload. Fires when the tools are reloaded.
-unload(function () {
-  gDevToolsBrowser.destroy();
-});
diff --git a/devtools/client/framework/devtools.js b/devtools/client/framework/devtools.js
index ff13f1f64459..3ec83cbdee87 100644
--- a/devtools/client/framework/devtools.js
+++ b/devtools/client/framework/devtools.js
@@ -18,7 +18,6 @@ const {defaultTools: DefaultTools, defaultThemes: DefaultThemes} =
 const EventEmitter = require("devtools/shared/event-emitter");
 const {JsonView} = require("devtools/client/jsonview/main");
 const AboutDevTools = require("devtools/client/framework/about-devtools-toolbox");
-const {when: unload} = require("sdk/system/unload");
 const {Task} = require("devtools/shared/task");
 
 const FORBIDDEN_IDS = new Set(["toolbox", ""]);
@@ -35,9 +34,6 @@ function DevTools() {
   // List of toolboxes that are still in process of creation
   this._creatingToolboxes = new Map(); // Map<target, toolbox Promise>
 
-  // destroy() is an observer's handler so we need to preserve context.
-  this.destroy = this.destroy.bind(this);
-
   // JSON Viewer for 'application/json' documents.
   JsonView.initialize();
 
@@ -45,8 +41,6 @@ function DevTools() {
 
   EventEmitter.decorate(this);
 
-  Services.obs.addObserver(this.destroy, "quit-application", false);
-
   // This is important step in initialization codepath where we are going to
   // start registering all default tools and themes: create menuitems, keys, emit
   // related events.
@@ -480,20 +474,23 @@ DevTools.prototype = {
   },
 
   /**
-   * Called to tear down a tools provider.
-   */
-  _teardown: function DT_teardown() {
-    for (let [target, toolbox] of this._toolboxes) {
-      toolbox.destroy();
-    }
-    AboutDevTools.unregister();
-  },
+   * Either the SDK Loader has been destroyed by the add-on contribution
+   * workflow, or firefox is shutting down.
 
-  /**
-   * All browser windows have been closed, tidy up remaining objects.
+   * @param {boolean} shuttingDown
+   *        True if firefox is currently shutting down. We may prevent doing
+   *        some cleanups to speed it up. Otherwise everything need to be
+   *        cleaned up in order to be able to load devtools again.
    */
-  destroy: function () {
-    Services.obs.removeObserver(this.destroy, "quit-application");
+  destroy: function ({ shuttingDown }) {
+    // Do not cleanup everything during firefox shutdown, but only when
+    // devtools are reloaded via the add-on contribution workflow.
+    if (!shuttingDown) {
+      for (let [target, toolbox] of this._toolboxes) {
+        toolbox.destroy();
+      }
+      AboutDevTools.unregister();
+    }
 
     for (let [key, tool] of this.getToolDefinitionMap()) {
       this.unregisterTool(key, true);
@@ -519,8 +516,3 @@ DevTools.prototype = {
 };
 
 const gDevTools = exports.gDevTools = new DevTools();
-
-// Watch for module loader unload. Fires when the tools are reloaded.
-unload(function () {
-  gDevTools._teardown();
-});