--- a/browser/base/content/browser-tabsintitlebar.js
+++ b/browser/base/content/browser-tabsintitlebar.js
@@ -37,16 +37,18 @@ var TabsInTitlebar = {
     this.onWidgetAdded = this.onWidgetRemoved = function(aWidgetId, aArea) {
       if (aArea == CustomizableUI.AREA_TABSTRIP || aArea == CustomizableUI.AREA_MENUBAR)
         this._update(true);
     };
     CustomizableUI.addListener(this);
 
     addEventListener("resolutionchange", this, false);
 
+    gDragSpaceObserver.init();
+
     this._update(true, true);
   },
 
   allowedBy(condition, allow) {
     if (allow) {
       if (condition in this._disallowed) {
         delete this._disallowed[condition];
         this._update(true);
@@ -272,16 +274,17 @@ var TabsInTitlebar = {
                   function(node) { node.style.width = width + "px"; });
   },
 
   uninit() {
     removeEventListener("resolutionchange", this);
     Services.prefs.removeObserver(this._prefName, this);
     this._menuObserver.disconnect();
     CustomizableUI.removeListener(this);
+    gDragSpaceObserver.uninit();
   }
 };
 
 function updateTitlebarDisplay() {
   if (AppConstants.platform == "macosx") {
     if (TabsInTitlebar.enabled) {
       document.documentElement.setAttribute("chromemargin", "0,-1,-1,-1");
       document.documentElement.removeAttribute("drawtitle");
@@ -298,8 +301,40 @@ function updateTitlebarDisplay() {
 }
 
 function onTitlebarMaxClick() {
   if (window.windowState == window.STATE_MAXIMIZED)
     window.restore();
   else
     window.maximize();
 }
+
+// Adds additional drag space to the window by listening to
+// the corresponding preference.
+var gDragSpaceObserver = {
+  pref: "browser.tabs.extraDragSpace",
+
+  init() {
+    this.update();
+    Services.prefs.addObserver(this.pref, this);
+  },
+
+  uninit() {
+    Services.prefs.removeObserver(this.pref, this);
+  },
+
+  observe(aSubject, aTopic, aPrefName) {
+    if (aTopic != "nsPref:changed" || aPrefName != this.pref) {
+      return;
+    }
+
+    this.update();
+  },
+
+  update() {
+    if (Services.prefs.getBoolPref(this.pref)) {
+      document.documentElement.setAttribute("extradragspace", "true");
+    } else {
+      document.documentElement.removeAttribute("extradragspace");
+    }
+    TabsInTitlebar.updateAppearance(true);
+  },
+};

--- a/browser/base/content/browser.js
+++ b/browser/base/content/browser.js
@@ -1291,20 +1291,16 @@ var gBrowserInit = {
     }
 
     gBrowser.updateBrowserRemoteness(initBrowser, isRemote, {
       remoteType, sameProcessAsFrameLoader
     });
 
     gUIDensity.init();
 
-    if (AppConstants.CAN_DRAW_IN_TITLEBAR) {
-      gDragSpaceObserver.init();
-    }
-
     // Hack to ensure that the about:home favicon is loaded
     // instantaneously, to avoid flickering and improve perceived performance.
     this._callWithURIToLoad(uriToLoad => {
       if (uriToLoad == "about:home") {
         gBrowser.setIcon(gBrowser.selectedTab, "chrome://branding/content/icon32.png");
       } else if (uriToLoad == "about:privatebrowsing") {
         gBrowser.setIcon(gBrowser.selectedTab, "chrome://browser/skin/privatebrowsing/favicon.svg");
       }
@@ -1844,20 +1840,16 @@ var gBrowserInit = {
       callback(uriToLoad);
     else
       uriToLoad.then(callback);
   },
 
   onUnload() {
     gUIDensity.uninit();
 
-    if (AppConstants.CAN_DRAW_IN_TITLEBAR) {
-      gDragSpaceObserver.uninit();
-    }
-
     TabsInTitlebar.uninit();
 
     // In certain scenarios it's possible for unload to be fired before onload,
     // (e.g. if the window is being closed after browser.js loads but before the
     // load completes). In that case, there's nothing to do here.
     if (!this._loadHandled)
       return;
 
@@ -5627,48 +5619,16 @@ var gTabletModePageCounter = {
     }
   },
 };
 
 function displaySecurityInfo() {
   BrowserPageInfo(null, "securityTab");
 }
 
-// Adds additional drag space to the window by listening to
-// the corresponding preference.
-var gDragSpaceObserver = {
-  pref: "browser.tabs.extraDragSpace",
-
-  init() {
-    this.update();
-    Services.prefs.addObserver(this.pref, this);
-  },
-
-  uninit() {
-    Services.prefs.removeObserver(this.pref, this);
-  },
-
-  observe(aSubject, aTopic, aPrefName) {
-    if (aTopic != "nsPref:changed" || aPrefName != this.pref) {
-      return;
-    }
-
-    this.update();
-  },
-
-  update() {
-    if (Services.prefs.getBoolPref(this.pref)) {
-      document.documentElement.setAttribute("extradragspace", "true");
-    } else {
-      document.documentElement.removeAttribute("extradragspace");
-    }
-    TabsInTitlebar.updateAppearance(true);
-  },
-};
-
 // Updates the UI density (for touch and compact mode) based on the uidensity pref.
 var gUIDensity = {
   MODE_NORMAL: 0,
   MODE_COMPACT: 1,
   MODE_TOUCH: 2,
   uiDensityPref: "browser.uidensity",
   autoTouchModePref: "browser.touchmode.auto",