diff --git a/browser/base/content/test/browser_tab_dragdrop.js b/browser/base/content/test/browser_tab_dragdrop.js
index 973454df401..04e4acdd7fa 100644
--- a/browser/base/content/test/browser_tab_dragdrop.js
+++ b/browser/base/content/test/browser_tab_dragdrop.js
@@ -61,9 +61,7 @@ function test()
 
       executeSoon(function () {
         var win = gBrowser.replaceTabWithWindow(t);
-        win.addEventListener("load", function () {
-          win.removeEventListener("load", arguments.callee, true);
-
+        whenDelayedStartupFinished(win, function () {
           // Verify that the original window now only has the initial tab left in it.
           is(gBrowser.tabs[0], tabs[0], "tab0");
           is(gBrowser.getBrowserForTab(gBrowser.tabs[0]).contentWindow.location, "about:blank", "tab0 uri");
@@ -82,7 +80,7 @@ function test()
             }, false);
             win.gBrowser.goBack();
           });
-        }, true);
+        });
       });
     }, true);
     b.loadURI("about:blank");
@@ -111,10 +109,10 @@ function test()
     gBrowser.getBrowserForTab(tabs[i]).addEventListener("load", fn(waitForLoad,i), true);
   }
 
-  setLocation(1, "data:text/html,<title>tab1</title><body>tab1<iframe>");
-  setLocation(2, "data:text/plain,tab2");
-  setLocation(3, "data:text/html,<title>tab3</title><body>tab3<iframe>");
-  setLocation(4, "data:text/html,<body onload='clicks=0' onclick='++clicks'>"+embed);
+  setLocation(1, "data:text/html;charset=utf-8,<title>tab1</title><body>tab1<iframe>");
+  setLocation(2, "data:text/plain;charset=utf-8,tab2");
+  setLocation(3, "data:text/html;charset=utf-8,<title>tab3</title><body>tab3<iframe>");
+  setLocation(4, "data:text/html;charset=utf-8,<body onload='clicks=0' onclick='++clicks'>"+embed);
   gBrowser.selectedTab = tabs[3];
 
 }
diff --git a/browser/base/content/test/social/browser_social_toolbar.js b/browser/base/content/test/social/browser_social_toolbar.js
index 2a648ade266..e06e3a57fbf 100644
--- a/browser/base/content/test/social/browser_social_toolbar.js
+++ b/browser/base/content/test/social/browser_social_toolbar.js
@@ -124,11 +124,14 @@ var tests = {
     let numIcons = Object.keys(Social.provider.ambientNotificationIcons).length;
     ok(numIcons == 3, "prevent adding more than 3 ambient notification icons");
 
-    let statusIcon = document.getElementById("social-provider-button").nextSibling;
+    let mButton = document.getElementById("social-mark-button");
+    let pButton = document.getElementById("social-provider-button");
     waitForCondition(function() {
-      statusIcon = document.getElementById("social-provider-button").nextSibling;
-      return !!statusIcon;
+      // wait for a new button to be inserted inbetween the provider and mark
+      // button
+      return pButton.nextSibling != mButton;
     }, function () {
+      let statusIcon = pButton.nextSibling;
       let badge = statusIcon.getAttribute("badge");
       is(badge, "42", "status value is correct");
       // If there is a counter, the aria-label should reflect it.
@@ -136,6 +139,7 @@ var tests = {
 
       ambience.counter = 0;
       Social.provider.setAmbientNotification(ambience);
+      statusIcon = pButton.nextSibling;
       badge = statusIcon.getAttribute("badge");
       is(badge, "", "status value is correct");
       // If there is no counter, the aria-label should be the same as the label
diff --git a/browser/components/sessionstore/src/SessionStore.jsm b/browser/components/sessionstore/src/SessionStore.jsm
index c43c6ecfb28..48285b1b3d0 100644
--- a/browser/components/sessionstore/src/SessionStore.jsm
+++ b/browser/components/sessionstore/src/SessionStore.jsm
@@ -2781,6 +2781,8 @@ let SessionStoreInternal = {
       return;
     }
 
+    TelemetryStopwatch.start("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
+
     // We're not returning from this before we end up calling restoreHistoryPrecursor
     // for this window, so make sure we send the SSWindowStateBusy event.
     this._setWindowStateBusy(aWindow);
@@ -2933,6 +2935,8 @@ let SessionStoreInternal = {
     // set smoothScroll back to the original value
     tabstrip.smoothScroll = smoothScroll;
 
+    TelemetryStopwatch.finish("FX_SESSION_RESTORE_RESTORE_WINDOW_MS");
+
     this._sendRestoreCompletedNotifications();
   },
 
diff --git a/build/automation.py.in b/build/automation.py.in
index 7dd4d77ac75..343a69885f3 100644
--- a/build/automation.py.in
+++ b/build/automation.py.in
@@ -488,7 +488,7 @@ class Automation(object):
         ldLibraryPath = ldLibraryPath + ":" + env[envVar]
       env[envVar] = ldLibraryPath
     elif self.IS_WIN32:
-      env["PATH"] = env["PATH"] + ";" + ldLibraryPath
+      env["PATH"] = env["PATH"] + ";" + str(ldLibraryPath)
 
     if crashreporter:
       env['MOZ_CRASHREPORTER_NO_REPORT'] = '1'
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 5b59068252d..7f67a613bed 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -5241,7 +5241,7 @@ class CGJsonifierMethod(CGSpecializedMethod):
                '  return false;\n'
                '}\n')
         for m in self.descriptor.interface.members:
-          if m.isAttr() and not m.isStatic():
+          if m.isAttr() and not m.isStatic() and m.type.isSerializable():
               ret += ('{ // scope for "temp"\n'
                       '  JS::Rooted<JS::Value> temp(cx);\n'
                       '  if (!get_%s(cx, obj, self, JSJitGetterCallArgs(&temp))) {\n'
diff --git a/dom/bindings/parser/WebIDL.py b/dom/bindings/parser/WebIDL.py
index 6fc4eca556d..55319c79128 100644
--- a/dom/bindings/parser/WebIDL.py
+++ b/dom/bindings/parser/WebIDL.py
@@ -1333,6 +1333,9 @@ class IDLType(IDLObject):
         # Should only call this on float types
         assert self.isFloat()
 
+    def isSerializable(self):
+        return False
+
     def tag(self):
         assert False # Override me!
 
@@ -1468,6 +1471,9 @@ class IDLNullableType(IDLType):
     def isUnion(self):
         return self.inner.isUnion()
 
+    def isSerializable(self):
+        return self.inner.isSerializable()
+
     def tag(self):
         return self.inner.tag()
 
@@ -1553,6 +1559,9 @@ class IDLSequenceType(IDLType):
     def isEnum(self):
         return False
 
+    def isSerializable(self):
+        return self.inner.isSerializable()
+
     def includesRestrictedFloat(self):
         return self.inner.includesRestrictedFloat()
 
@@ -1602,6 +1611,9 @@ class IDLUnionType(IDLType):
     def isUnion(self):
         return True
 
+    def isSerializable(self):
+        return all(m.isSerializable() for m in self.memberTypes)
+
     def includesRestrictedFloat(self):
         return any(t.includesRestrictedFloat() for t in self.memberTypes)
 
@@ -1932,6 +1944,19 @@ class IDLWrapperType(IDLType):
     def isEnum(self):
         return isinstance(self.inner, IDLEnum)
 
+    def isSerializable(self):
+        if self.isInterface():
+            if self.inner.isExternal():
+                return False
+            return any(m.isMethod() and m.isJsonifier() for m in self.inner.members)
+        elif self.isEnum():
+            return True
+        elif self.isDictionary():
+            return all(m.isSerializable() for m in self.inner.members)
+        else:
+            raise WebIDLError("IDLWrapperType wraps type %s that we don't know if "
+                              "is serializable" % type(self.inner), [self.location])
+
     def resolveType(self, parentScope):
         assert isinstance(parentScope, IDLScope)
         self.inner.resolve(parentScope)
@@ -2130,6 +2155,9 @@ class IDLBuiltinType(IDLType):
         return self._typeTag == IDLBuiltinType.Types.unrestricted_float or \
                self._typeTag == IDLBuiltinType.Types.unrestricted_double
 
+    def isSerializable(self):
+        return self.isPrimitive() or self.isDOMString() or self.isDate()
+
     def includesRestrictedFloat(self):
         return self.isFloat() and not self.isUnrestricted()
 
diff --git a/dom/bindings/test/TestBindingHeader.h b/dom/bindings/test/TestBindingHeader.h
index 0a247de67b1..2fa3edb0d04 100644
--- a/dom/bindings/test/TestBindingHeader.h
+++ b/dom/bindings/test/TestBindingHeader.h
@@ -608,6 +608,12 @@ public:
   TestInterface* PutForwardsAttr();
   TestInterface* PutForwardsAttr2();
   TestInterface* PutForwardsAttr3();
+  JS::Value JsonifierShouldSkipThis(JSContext*);
+  void SetJsonifierShouldSkipThis(JSContext*, JS::Rooted<JS::Value>&);
+  TestParentInterface* JsonifierShouldSkipThis2();
+  void SetJsonifierShouldSkipThis2(TestParentInterface&);
+  TestCallbackInterface* JsonifierShouldSkipThis3();
+  void SetJsonifierShouldSkipThis3(TestCallbackInterface&);
   void ThrowingMethod(ErrorResult& aRv);
   bool GetThrowingAttr(ErrorResult& aRv) const;
   void SetThrowingAttr(bool arg, ErrorResult& aRv);
diff --git a/dom/bindings/test/TestCodeGen.webidl b/dom/bindings/test/TestCodeGen.webidl
index 193aaf085fe..fd2d6a2fbcf 100644
--- a/dom/bindings/test/TestCodeGen.webidl
+++ b/dom/bindings/test/TestCodeGen.webidl
@@ -583,6 +583,10 @@ interface TestInterface {
                             optional TestInterface? arg2 = null,
                             optional Dict arg3, optional double arg4 = 5.0,
                             optional float arg5);
+
+  attribute any jsonifierShouldSkipThis;
+  attribute TestParentInterface jsonifierShouldSkipThis2;
+  attribute TestCallbackInterface jsonifierShouldSkipThis3;
   jsonifier;
 
   // If you add things here, add them to TestExampleGen and TestJSImplGen as well
diff --git a/dom/bindings/test/TestExampleGen.webidl b/dom/bindings/test/TestExampleGen.webidl
index ee75b70e48d..1750eb5ed7b 100644
--- a/dom/bindings/test/TestExampleGen.webidl
+++ b/dom/bindings/test/TestExampleGen.webidl
@@ -480,6 +480,9 @@ interface TestExampleInterface {
                             optional TestInterface? arg2 = null,
                             optional Dict arg3, optional double arg4 = 5.0,
                             optional float arg5);
+  attribute any jsonifierShouldSkipThis;
+  attribute TestParentInterface jsonifierShouldSkipThis2;
+  attribute TestCallbackInterface jsonifierShouldSkipThis3;
   jsonifier;
 
   // If you add things here, add them to TestCodeGen and TestJSImplGen as well
diff --git a/dom/bindings/test/TestJSImplGen.webidl b/dom/bindings/test/TestJSImplGen.webidl
index 99b755492a9..4b58009e99e 100644
--- a/dom/bindings/test/TestJSImplGen.webidl
+++ b/dom/bindings/test/TestJSImplGen.webidl
@@ -472,6 +472,9 @@ interface TestJSImplInterface {
                             optional TestInterface? arg2 = null,
                             optional Dict arg3, optional double arg4 = 5.0,
                             optional float arg5);
+  attribute any jsonifierShouldSkipThis;
+  attribute TestParentInterface jsonifierShouldSkipThis2;
+  attribute TestCallbackInterface jsonifierShouldSkipThis3;
   jsonifier;
 
   // If you add things here, add them to TestCodeGen as well
diff --git a/testing/mochitest/runtests.py b/testing/mochitest/runtests.py
index 14e3ae123f5..6d8b8163b9b 100644
--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -69,7 +69,7 @@ class MochitestServer:
     env["ASAN_OPTIONS"] = "quarantine_size=1:redzone=32"
 
     if mozinfo.isWin:
-      env["PATH"] = env["PATH"] + ";" + self._xrePath
+      env["PATH"] = env["PATH"] + ";" + str(self._xrePath)
 
     args = ["-g", self._xrePath,
             "-v", "170",
diff --git a/toolkit/components/telemetry/Histograms.json b/toolkit/components/telemetry/Histograms.json
index 7ad2c705d29..991461eacf0 100644
--- a/toolkit/components/telemetry/Histograms.json
+++ b/toolkit/components/telemetry/Histograms.json
@@ -2545,6 +2545,13 @@
     "extended_statistics_ok": true,
     "description": "Session restore: Time to make a backup copy of the session file (ms)"
   },
+  "FX_SESSION_RESTORE_RESTORE_WINDOW_MS": {
+    "kind": "exponential",
+    "high": "3000",
+    "n_buckets": 10,
+    "extended_statistics_ok": true,
+    "description": "Session restore: Time spent blocking the main thread while restoring a window state (ms)"
+  },
   "INNERWINDOWS_WITH_MUTATION_LISTENERS": {
     "kind": "boolean",
     "description": "Deleted or to-be-reused innerwindow which has had mutation event listeners."
diff --git a/widget/gtk2/gtk2drawing.c b/widget/gtk2/gtk2drawing.c
index 0c2076ea965..7c8413d02c2 100644
--- a/widget/gtk2/gtk2drawing.c
+++ b/widget/gtk2/gtk2drawing.c
@@ -1765,27 +1765,6 @@ moz_gtk_treeview_expander_paint(GdkDrawable* drawable, GdkRectangle* rect,
     return MOZ_GTK_SUCCESS;
 }
 
-static gint
-moz_gtk_expander_paint(GdkDrawable* drawable, GdkRectangle* rect,
-                       GdkRectangle* cliprect, GtkWidgetState* state,
-                       GtkExpanderStyle expander_state,
-                       GtkTextDirection direction)
-{
-    GtkStyle *style;
-    GtkStateType state_type = ConvertGtkState(state);
-
-    ensure_expander_widget();
-    gtk_widget_set_direction(gExpanderWidget, direction);
-
-    style = gExpanderWidget->style;
-
-    TSOffsetStyleGCs(style, rect->x, rect->y);
-    gtk_paint_expander(style, drawable, state_type, cliprect, gExpanderWidget, "expander",
-                       rect->x + rect->width / 2, rect->y + rect->height / 2, expander_state);
-
-    return MOZ_GTK_SUCCESS;
-}
-
 static gint
 moz_gtk_combo_box_paint(GdkDrawable* drawable, GdkRectangle* rect,
                         GdkRectangle* cliprect, GtkWidgetState* state,
@@ -2969,7 +2948,6 @@ moz_gtk_get_widget_border(GtkThemeWidgetType widget, gint* left, gint* top,
     case MOZ_GTK_PROGRESS_CHUNK:
     case MOZ_GTK_PROGRESS_CHUNK_INDETERMINATE:
     case MOZ_GTK_PROGRESS_CHUNK_VERTICAL_INDETERMINATE:
-    case MOZ_GTK_EXPANDER:
     case MOZ_GTK_TREEVIEW_EXPANDER:
     case MOZ_GTK_TOOLBAR_SEPARATOR:
     case MOZ_GTK_MENUSEPARATOR:
@@ -3256,10 +3234,6 @@ moz_gtk_widget_paint(GtkThemeWidgetType widget, GdkDrawable* drawable,
         return moz_gtk_treeview_expander_paint(drawable, rect, cliprect, state,
                                                (GtkExpanderStyle) flags, direction);
         break;
-    case MOZ_GTK_EXPANDER:
-        return moz_gtk_expander_paint(drawable, rect, cliprect, state,
-                                      (GtkExpanderStyle) flags, direction);
-        break;
     case MOZ_GTK_ENTRY:
         ensure_entry_widget();
         return moz_gtk_entry_paint(drawable, rect, cliprect, state,
diff --git a/widget/gtk2/gtk3drawing.c b/widget/gtk2/gtk3drawing.c
index 324d3ba7f18..57122df1319 100644
--- a/widget/gtk2/gtk3drawing.c
+++ b/widget/gtk2/gtk3drawing.c
@@ -1570,6 +1570,8 @@ moz_gtk_tree_header_sort_arrow_paint(cairo_t *cr, GdkRectangle* rect,
     return MOZ_GTK_SUCCESS;
 }
 
+/* See gtk_expander_paint() for reference. 
+ */
 static gint
 moz_gtk_treeview_expander_paint(cairo_t *cr, GdkRectangle* rect,
                                 GtkWidgetState* state,
@@ -1577,6 +1579,7 @@ moz_gtk_treeview_expander_paint(cairo_t *cr, GdkRectangle* rect,
                                 GtkTextDirection direction)
 {
     GtkStyleContext *style;
+    GtkStateFlags    state_flags;
 
     ensure_tree_view_widget();
     gtk_widget_set_direction(gTreeViewWidget, direction);
@@ -1584,34 +1587,25 @@ moz_gtk_treeview_expander_paint(cairo_t *cr, GdkRectangle* rect,
     style = gtk_widget_get_style_context(gTreeViewWidget);
     gtk_style_context_save(style);
     gtk_style_context_add_class(style, GTK_STYLE_CLASS_EXPANDER);
-    /* Because the frame we get is of the entire treeview, we can't get the precise
-     * event state of one expander, thus rendering hover and active feedback useless. */
-    gtk_style_context_set_state(style, GetStateFlagsFromGtkWidgetState(state));
+
+    state_flags = GetStateFlagsFromGtkWidgetState(state);
+
+    /* GTK_STATE_FLAG_ACTIVE controls expanded/colapsed state rendering
+     * in gtk_render_expander()
+     */
+    if (expander_state == GTK_EXPANDER_EXPANDED) 
+        state_flags |= GTK_STATE_FLAG_ACTIVE;
+    else
+        state_flags &= ~(GTK_STATE_FLAG_ACTIVE);
+
+    gtk_style_context_set_state(style, state_flags);
+
     gtk_render_expander(style, cr,
-                        rect->x + rect->width / 2, rect->y + rect->height / 2,
-                        rect->width, rect->height);
-    gtk_style_context_restore(style);
-    return MOZ_GTK_SUCCESS;
-}
+                        rect->x,
+                        rect->y,
+                        rect->width,
+                        rect->height);
 
-static gint
-moz_gtk_expander_paint(cairo_t *cr, GdkRectangle* rect,
-                       GtkWidgetState* state,
-                       GtkExpanderStyle expander_state,
-                       GtkTextDirection direction)
-{
-    GtkStyleContext *style;
-
-    ensure_expander_widget();
-    gtk_widget_set_direction(gExpanderWidget, direction);
-
-    style = gtk_widget_get_style_context(gExpanderWidget);
-    gtk_style_context_save(style);
-    gtk_style_context_add_class(style, GTK_STYLE_CLASS_EXPANDER);
-    gtk_style_context_set_state(style, GetStateFlagsFromGtkWidgetState(state));
-    gtk_render_expander(style, cr, 
-                        rect->x + rect->width / 2, rect->y + rect->height / 2,
-						rect->width, rect->height);
     gtk_style_context_restore(style);
     return MOZ_GTK_SUCCESS;
 }
@@ -2828,7 +2822,6 @@ moz_gtk_get_widget_border(GtkThemeWidgetType widget, gint* left, gint* top,
     case MOZ_GTK_PROGRESS_CHUNK:
     case MOZ_GTK_PROGRESS_CHUNK_INDETERMINATE:
     case MOZ_GTK_PROGRESS_CHUNK_VERTICAL_INDETERMINATE:
-    case MOZ_GTK_EXPANDER:
     case MOZ_GTK_TREEVIEW_EXPANDER:
     case MOZ_GTK_TOOLBAR_SEPARATOR:
     case MOZ_GTK_MENUSEPARATOR:
@@ -3134,10 +3127,6 @@ moz_gtk_widget_paint(GtkThemeWidgetType widget, cairo_t *cr,
         return moz_gtk_treeview_expander_paint(cr, rect, state,
                                                (GtkExpanderStyle) flags, direction);
         break;
-    case MOZ_GTK_EXPANDER:
-        return moz_gtk_expander_paint(cr, rect, state,
-                                      (GtkExpanderStyle) flags, direction);
-        break;
     case MOZ_GTK_ENTRY:
         ensure_entry_widget();
         return moz_gtk_entry_paint(cr, rect, state,
diff --git a/widget/gtk2/gtkdrawing.h b/widget/gtk2/gtkdrawing.h
index 6508d27cf56..5d38574bd7c 100644
--- a/widget/gtk2/gtkdrawing.h
+++ b/widget/gtk2/gtkdrawing.h
@@ -161,8 +161,6 @@ typedef enum {
   MOZ_GTK_TREE_HEADER_SORTARROW,
   /* Paints an expander for a GtkTreeView */
   MOZ_GTK_TREEVIEW_EXPANDER,
-  /* Paints a GtkExpander */
-  MOZ_GTK_EXPANDER,
   /* Paints the background of the menu bar. */
   MOZ_GTK_MENUBAR,
   /* Paints the background of menus, context menus. */
