--- a/gfx/gl/GLContextGLX.h
+++ b/gfx/gl/GLContextGLX.h
@@ -6,16 +6,18 @@
 
 #ifndef GLCONTEXTGLX_H_
 #define GLCONTEXTGLX_H_
 
 #include "GLContext.h"
 #include "GLXLibrary.h"
 #include "mozilla/X11Util.h"
 
+class gfxXlibSurface;
+
 namespace mozilla {
 namespace gl {
 
 class GLContextGLX : public GLContext
 {
 public:
     MOZ_DECLARE_REFCOUNTED_VIRTUAL_TYPENAME(GLContextGLX, override)
     static already_AddRefed<GLContextGLX>

--- a/widget/gtk/mozgtk/mozgtk.c
+++ b/widget/gtk/mozgtk/mozgtk.c
@@ -130,16 +130,18 @@ STUB(gdk_x11_display_get_user_time)
 STUB(gdk_x11_display_get_xdisplay)
 STUB(gdk_x11_get_default_root_xwindow)
 STUB(gdk_x11_get_default_xdisplay)
 STUB(gdk_x11_get_server_time)
 STUB(gdk_x11_get_xatom_by_name)
 STUB(gdk_x11_get_xatom_by_name_for_display)
 STUB(gdk_x11_lookup_xdisplay)
 STUB(gdk_x11_screen_get_xscreen)
+STUB(gdk_x11_screen_get_screen_number)
+STUB(gdk_x11_screen_lookup_visual)
 STUB(gdk_x11_screen_supports_net_wm_hint)
 STUB(gdk_x11_visual_get_xvisual)
 STUB(gdk_x11_window_foreign_new_for_display)
 STUB(gdk_x11_window_lookup_for_display)
 STUB(gdk_x11_window_set_user_time)
 STUB(gdk_x11_xatom_to_atom)
 STUB(gdk_x11_set_sm_client_id)
 STUB(gtk_accel_label_new)

--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -111,16 +111,17 @@ using namespace mozilla::widget;
 #include "GLContextProvider.h"
 #include "mozilla/gfx/2D.h"
 #include "mozilla/gfx/HelpersCairo.h"
 #include "mozilla/gfx/GPUProcessManager.h"
 #include "mozilla/layers/CompositorBridgeParent.h"
 #include "mozilla/layers/CompositorThread.h"
 
 #ifdef MOZ_X11
+#include "GLContextGLX.h" // for GLContextGLX::FindVisual()
 #include "GtkCompositorWidget.h"
 #include "gfxXlibSurface.h"
 #include "WindowSurfaceX11Image.h"
 #include "WindowSurfaceX11SHM.h"
 #include "WindowSurfaceXRender.h"
 #endif // MOZ_X11
 #ifdef MOZ_WAYLAND
 #include "nsIClipboard.h"
@@ -134,16 +135,17 @@ using namespace mozilla::widget;
 
 #include <dlfcn.h>
 
 using namespace mozilla;
 using namespace mozilla::gfx;
 using namespace mozilla::widget;
 using namespace mozilla::layers;
 using mozilla::gl::GLContext;
+using mozilla::gl::GLContextGLX;
 
 // Don't put more than this many rects in the dirty region, just fluff
 // out to the bounding-box if there are more
 #define MAX_RECTS_IN_REGION 100
 
 const gint kEvents = GDK_EXPOSURE_MASK | GDK_STRUCTURE_MASK |
                      GDK_VISIBILITY_NOTIFY_MASK |
                      GDK_ENTER_NOTIFY_MASK | GDK_LEAVE_NOTIFY_MASK |
@@ -3635,21 +3637,40 @@ nsWindow::Create(nsIWidget* aParent,
         bool useAlphaVisual = (mWindowType == eWindowType_popup &&
                                aInitData->mSupportTranslucency);
 
         // mozilla.widget.use-argb-visuals is a hidden pref defaulting to false
         // to allow experimentation
         if (Preferences::GetBool("mozilla.widget.use-argb-visuals", false))
             useAlphaVisual = true;
 
-        // We need to select an ARGB visual here instead of in
-        // SetTransparencyMode() because it has to be done before the
-        // widget is realized.  An ARGB visual is only useful if we
-        // are on a compositing window manager.
-        if (useAlphaVisual) {
+        bool useWebRender = gfxPlatform::Initialized() &&
+            gfx::gfxVars::UseWebRender() &&
+            AllowWebRenderForThisWindow();
+
+        // If using WebRender on X11, we need to select a visual with a depth buffer,
+        // as well as an alpha channel if transparency is requested. This must be done
+        // before the widget is realized.
+        if (mIsX11Display && useWebRender) {
+            auto display =
+                GDK_DISPLAY_XDISPLAY(gtk_widget_get_display(mShell));
+            auto screen = gtk_widget_get_screen(mShell);
+            int screenNumber = GDK_SCREEN_XNUMBER(screen);
+            int visualId = 0;
+
+            if (GLContextGLX::FindVisual(display, screenNumber,
+                                         useWebRender, useAlphaVisual,
+                                         &visualId)) {
+                // If we're using CSD, rendering will go through mContainer, but
+                // it will inherit this visual as it is a child of mShell.
+                gtk_widget_set_visual(mShell,
+                                      gdk_x11_screen_lookup_visual(screen,
+                                                                   visualId));
+            }
+        } else if (useAlphaVisual) {
             GdkScreen *screen = gtk_widget_get_screen(mShell);
             if (gdk_screen_is_composited(screen)) {
                 GdkVisual *visual = gdk_screen_get_rgba_visual(screen);
                 gtk_widget_set_visual(mShell, visual);
             }
         }
 
         // We only move a general managed toplevel window if someone has
@@ -3754,17 +3775,17 @@ nsWindow::Create(nsIWidget* aParent,
         // Create a container to hold child windows and child GtkWidgets.
         GtkWidget *container = moz_container_new();
         mContainer = MOZ_CONTAINER(container);
 
         // "csd" style is set when widget is realized so we need to call
         // it explicitly now.
         gtk_widget_realize(mShell);
 
-        /* There are two cases here:
+        /* There are several cases here:
          *
          * 1) We're running on Gtk+ without client side decorations.
          *    Content is rendered to mShell window and we listen
          *    to the Gtk+ events on mShell
          * 2) We're running on Gtk+ and client side decorations
          *    are drawn by Gtk+ to mShell. Content is rendered to mContainer
          *    and we listen to the Gtk+ events on mContainer.
          * 3) We're running on Wayland. All gecko content is rendered