diff --git a/widget/gtk/CompositorWidgetParent.cpp b/widget/gtk/CompositorWidgetParent.cpp
index 4382ccf..9986146 100644
--- a/widget/gtk/CompositorWidgetParent.cpp
+++ b/widget/gtk/CompositorWidgetParent.cpp
@@ -6,9 +6,9 @@
 #include "CompositorWidgetParent.h"
 #include "mozilla/Unused.h"
 #include "mozilla/widget/PlatformWidgetTypes.h"
+#include "nsWindow.h"
 
-namespace mozilla {
-namespace widget {
+namespace mozilla::widget {
 
 CompositorWidgetParent::CompositorWidgetParent(
     const CompositorWidgetInitData& aInitData,
@@ -51,5 +51,4 @@ mozilla::ipc::IPCResult CompositorWidgetParent::RecvEnableRendering(
   return IPC_OK();
 }
 
-}  // namespace widget
-}  // namespace mozilla
+}  // namespace mozilla::widget
diff --git a/widget/gtk/GtkCompositorWidget.cpp b/widget/gtk/GtkCompositorWidget.cpp
index 07a1226..0a1d888 100644
--- a/widget/gtk/GtkCompositorWidget.cpp
+++ b/widget/gtk/GtkCompositorWidget.cpp
@@ -5,6 +5,7 @@
 
 #include "GtkCompositorWidget.h"
 
+#include "mozilla/gfx/gfxVars.h"
 #include "mozilla/layers/CompositorThread.h"
 #include "mozilla/widget/InProcessCompositorWidget.h"
 #include "mozilla/widget/PlatformWidgetTypes.h"
diff --git a/widget/gtk/IMContextWrapper.cpp b/widget/gtk/IMContextWrapper.cpp
index cc84d40..e2180f5 100644
--- a/widget/gtk/IMContextWrapper.cpp
+++ b/widget/gtk/IMContextWrapper.cpp
@@ -7,6 +7,7 @@
 #include "mozilla/Logging.h"
 #include "nsString.h"
 #include "prtime.h"
+#include "prenv.h"
 
 #include "IMContextWrapper.h"
 #include "nsGtkKeyUtils.h"
diff --git a/widget/gtk/InProcessGtkCompositorWidget.cpp b/widget/gtk/InProcessGtkCompositorWidget.cpp
index 4158118..bffd6f5 100644
--- a/widget/gtk/InProcessGtkCompositorWidget.cpp
+++ b/widget/gtk/InProcessGtkCompositorWidget.cpp
@@ -8,10 +8,10 @@
 #include "mozilla/widget/PlatformWidgetTypes.h"
 
 #include "InProcessGtkCompositorWidget.h"
+#include "VsyncDispatcher.h"
 #include "nsWindow.h"
 
-namespace mozilla {
-namespace widget {
+namespace mozilla::widget {
 
 /* static */
 RefPtr<CompositorWidget> CompositorWidget::CreateLocal(
@@ -41,5 +41,4 @@ void InProcessGtkCompositorWidget::ObserveVsync(VsyncObserver* aObserver) {
   }
 }
 
-}  // namespace widget
-}  // namespace mozilla
+}  // namespace mozilla::widget
diff --git a/widget/gtk/MPRISServiceHandler.cpp b/widget/gtk/MPRISServiceHandler.cpp
index ad85082..e21e46f 100644
--- a/widget/gtk/MPRISServiceHandler.cpp
+++ b/widget/gtk/MPRISServiceHandler.cpp
@@ -12,6 +12,7 @@
 
 #include "MPRISInterfaceDescription.h"
 #include "mozilla/dom/MediaControlUtils.h"
+#include "mozilla/GRefPtr.h"
 #include "mozilla/GUniquePtr.h"
 #include "mozilla/UniquePtrExtensions.h"
 #include "mozilla/Maybe.h"
diff --git a/widget/gtk/WindowSurfaceX11.cpp b/widget/gtk/WindowSurfaceX11.cpp
index a32cc12..36b238a 100644
--- a/widget/gtk/WindowSurfaceX11.cpp
+++ b/widget/gtk/WindowSurfaceX11.cpp
@@ -6,10 +6,8 @@
 
 #include "WindowSurfaceX11.h"
 #include "gfxPlatform.h"
-#include "X11UndefineNone.h"
 
-namespace mozilla {
-namespace widget {
+namespace mozilla::widget {
 
 WindowSurfaceX11::WindowSurfaceX11(Display* aDisplay, Window aWindow,
                                    Visual* aVisual, unsigned int aDepth)
@@ -46,5 +44,4 @@ gfx::SurfaceFormat WindowSurfaceX11::GetVisualFormat(const Visual* aVisual,
   return gfx::SurfaceFormat::UNKNOWN;
 }
 
-}  // namespace widget
-}  // namespace mozilla
+}  // namespace mozilla::widget
diff --git a/widget/gtk/WindowSurfaceX11.h b/widget/gtk/WindowSurfaceX11.h
index d297ec6..dda17bf 100644
--- a/widget/gtk/WindowSurfaceX11.h
+++ b/widget/gtk/WindowSurfaceX11.h
@@ -13,9 +13,9 @@
 #  include "mozilla/gfx/Types.h"
 
 #  include <X11/Xlib.h>
+#  include "X11UndefineNone.h"
 
-namespace mozilla {
-namespace widget {
+namespace mozilla::widget {
 
 class WindowSurfaceX11 : public WindowSurface {
  public:
@@ -33,8 +33,7 @@ class WindowSurfaceX11 : public WindowSurface {
   const gfx::SurfaceFormat mFormat;
 };
 
-}  // namespace widget
-}  // namespace mozilla
+}  // namespace mozilla::widget
 
 #endif  // MOZ_X11
 #endif  // _MOZILLA_WIDGET_GTK_WINDOW_SURFACE_X11_H
diff --git a/widget/gtk/moz.build b/widget/gtk/moz.build
index 5218c7d..2e578b9 100644
--- a/widget/gtk/moz.build
+++ b/widget/gtk/moz.build
@@ -187,6 +187,5 @@ if CONFIG["MOZ_ENABLE_DBUS"]:
         "AsyncDBus.cpp",
     ]
     CXXFLAGS += CONFIG["MOZ_DBUS_GLIB_CFLAGS"]
-CXXFLAGS += ["-Werror=switch"]
 
-REQUIRES_UNIFIED_BUILD = True
+CXXFLAGS += ["-Werror=switch"]
diff --git a/widget/gtk/mozgtk/mozgtk.c b/widget/gtk/mozgtk/mozgtk.c
index d7dbbc6..8c73c89 100644
--- a/widget/gtk/mozgtk/mozgtk.c
+++ b/widget/gtk/mozgtk/mozgtk.c
@@ -6,6 +6,12 @@
 
 #include "mozilla/Types.h"
 
+// Dummy call to gtk3 library to prevent the linker from removing
+// the gtk3 dependency with --as-needed.
+// see toolkit/library/moz.build for details.
+MOZ_EXPORT void gdk_display_get_default();
+MOZ_EXPORT void mozgtk_linker_holder(void) { gdk_display_get_default(); }
+
 #ifdef MOZ_X11
 #  include <X11/Xlib.h>
 // Bug 1271100
diff --git a/widget/gtk/nsApplicationChooser.cpp b/widget/gtk/nsApplicationChooser.cpp
index 2ebb62f..6752c52 100644
--- a/widget/gtk/nsApplicationChooser.cpp
+++ b/widget/gtk/nsApplicationChooser.cpp
@@ -11,6 +11,7 @@
 #include "WidgetUtils.h"
 #include "nsIMIMEInfo.h"
 #include "nsIWidget.h"
+#include "nsIFile.h"
 #include "nsCExternalHandlerService.h"
 #include "nsComponentManagerUtils.h"
 #include "nsGtkUtils.h"
diff --git a/widget/gtk/nsClipboard.cpp b/widget/gtk/nsClipboard.cpp
index 555e8ce..fd49d92 100644
--- a/widget/gtk/nsClipboard.cpp
+++ b/widget/gtk/nsClipboard.cpp
@@ -31,6 +31,7 @@
 #include "nsIObserverService.h"
 #include "mozilla/Services.h"
 #include "mozilla/RefPtr.h"
+#include "mozilla/GRefPtr.h"
 #include "mozilla/SchedulerGroup.h"
 #include "mozilla/StaticPrefs_widget.h"
 #include "mozilla/TimeStamp.h"
@@ -39,7 +40,9 @@
 #include "imgIContainer.h"
 
 #include <gtk/gtk.h>
-#include <gtk/gtkx.h>
+#if defined(MOZ_X11)
+#  include <gtk/gtkx.h>
+#endif
 
 #include "mozilla/Encoding.h"
 
diff --git a/widget/gtk/nsGtkKeyUtils.h b/widget/gtk/nsGtkKeyUtils.h
index 6fcc3e9..8462b6d 100644
--- a/widget/gtk/nsGtkKeyUtils.h
+++ b/widget/gtk/nsGtkKeyUtils.h
@@ -20,6 +20,7 @@
 #  include <gdk/gdkwayland.h>
 #  include <xkbcommon/xkbcommon.h>
 #endif
+#include "X11UndefineNone.h"
 
 class nsWindow;
 
diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp
index e14c4f4..3bd659d 100644
--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -267,6 +267,9 @@ static SystemTimeConverter<guint32>& TimeConverter() {
 
 bool nsWindow::sTransparentMainWindow = false;
 
+/* forward declare from mozgtk */
+MOZ_EXPORT extern "C" void mozgtk_linker_holder(void);
+
 namespace mozilla {
 
 #ifdef MOZ_X11
@@ -426,6 +429,10 @@ nsWindow::nsWindow()
     }
 #endif
   }
+  // Dummy call to mozgtk to prevent the linker from removing
+  // the dependency with --as-needed.
+  // see toolkit/library/moz.build for details.
+  mozgtk_linker_holder();
 }
 
 nsWindow::~nsWindow() {
@@ -5302,10 +5309,6 @@ void nsWindow::ConfigureGdkWindow() {
     // tearing because Gecko does not align its framebuffer updates with
     // vblank.
     SetCompositorHint(GTK_WIDGET_COMPOSIDED_ENABLED);
-
-    // Dummy call to a function in mozgtk to prevent the linker from removing
-    // the dependency with --as-needed.
-    XShmQueryExtension(DefaultXDisplay());
   }
 #endif
 #ifdef MOZ_WAYLAND