This is a composition of these patches for Firefox 60:

https://bugzilla.mozilla.org/show_bug.cgi?id=1441873

https://bugzilla.mozilla.org/show_bug.cgi?id=1441665

https://bugzilla.mozilla.org/show_bug.cgi?id=1456898

https://bugzilla.mozilla.org/show_bug.cgi?id=1457309

https://bugzilla.mozilla.org/show_bug.cgi?id=1457691

which fix popup window placement at CSD window mode.

diff --git a/widget/gtk/nsLookAndFeel.cpp b/widget/gtk/nsLookAndFeel.cpp

--- a/widget/gtk/nsLookAndFeel.cpp

+++ b/widget/gtk/nsLookAndFeel.cpp

@@ -1076,19 +1076,18 @@ nsLookAndFeel::EnsureInit()

                          nullptr);

     GetSystemFontInfo(gtk_widget_get_style_context(entry),

                       &mFieldFontName, &mFieldFontStyle);

     gtk_widget_destroy(window);

     g_object_unref(labelWidget);

-    // Require GTK 3.10 for GtkHeaderBar support and compatible window manager.

-    mCSDAvailable = (gtk_check_version(3, 10, 0) == nullptr &&

-        nsWindow::GetCSDSupportLevel() != nsWindow::CSD_SUPPORT_NONE);

+    mCSDAvailable =

+        nsWindow::GetSystemCSDSupportLevel() != nsWindow::CSD_SUPPORT_NONE;

     mCSDCloseButton = false;

     mCSDMinimizeButton = false;

     mCSDMaximizeButton = false;

     // We need to initialize whole CSD config explicitly because it's queried

     // as -moz-gtk* media features.

     WidgetNodeType buttonLayout[TOOLBAR_BUTTONS];

diff --git a/widget/gtk/nsWindow.h b/widget/gtk/nsWindow.h

--- a/widget/gtk/nsWindow.h

+++ b/widget/gtk/nsWindow.h

@@ -395,28 +395,26 @@ public:

     // From GDK

     int GdkCoordToDevicePixels(gint coord);

     LayoutDeviceIntPoint GdkPointToDevicePixels(GdkPoint point);

     LayoutDeviceIntPoint GdkEventCoordsToDevicePixels(gdouble x, gdouble y);

     LayoutDeviceIntRect GdkRectToDevicePixels(GdkRectangle rect);

     virtual bool WidgetTypeSupportsAcceleration() override;

-    bool DoDrawTitlebar() const;

-

     typedef enum { CSD_SUPPORT_SYSTEM,    // CSD including shadows

                    CSD_SUPPORT_CLIENT,    // CSD without shadows

                    CSD_SUPPORT_NONE,      // WM does not support CSD at all

                    CSD_SUPPORT_UNKNOWN

     } CSDSupportLevel;

     /**

      * Get the support of Client Side Decoration by checking

      * the XDG_CURRENT_DESKTOP environment variable.

      */

-    static CSDSupportLevel GetCSDSupportLevel();

+    static CSDSupportLevel GetSystemCSDSupportLevel();

 protected:

     virtual ~nsWindow();

     // event handling code

     void DispatchActivateEvent(void);

     void DispatchDeactivateEvent(void);

     void DispatchResized();

@@ -512,19 +510,21 @@ private:

     int                 mXDepth;

     mozilla::widget::WindowSurfaceProvider mSurfaceProvider;

 #endif

     // Upper bound on pending ConfigureNotify events to be dispatched to the

     // window. See bug 1225044.

     unsigned int mPendingConfigures;

-    bool               mIsCSDAvailable;

+    // Window titlebar rendering mode, CSD_SUPPORT_NONE if it's disabled

+    // for this window.

+    CSDSupportLevel    mCSDSupportLevel;

     // If true, draw our own window titlebar.

-    bool               mIsCSDEnabled;

+    bool               mDrawInTitlebar;

     // Draggable titlebar region maintained by UpdateWindowDraggingRegion

     LayoutDeviceIntRegion mDraggableRegion;

 #ifdef ACCESSIBILITY

     RefPtr<mozilla::a11y::Accessible> mRootAccessible;

     /**

      * Request to create the accessible for this window if it is top level.

diff --git a/widget/gtk/nsWindow.cpp b/widget/gtk/nsWindow.cpp

--- a/widget/gtk/nsWindow.cpp

+++ b/widget/gtk/nsWindow.cpp

@@ -474,18 +474,18 @@ nsWindow::nsWindow()

     mTransparencyBitmapWidth  = 0;

     mTransparencyBitmapHeight = 0;

 #if GTK_CHECK_VERSION(3,4,0)

     mLastScrollEventTime = GDK_CURRENT_TIME;

 #endif

     mPendingConfigures = 0;

-    mIsCSDAvailable = false;

-    mIsCSDEnabled = false;

+    mCSDSupportLevel = CSD_SUPPORT_NONE;

+    mDrawInTitlebar = false;

 }

 nsWindow::~nsWindow()

 {

     LOG(("nsWindow::~nsWindow() [%p]\n", (void *)this));

     delete[] mTransparencyBitmap;

     mTransparencyBitmap = nullptr;

@@ -2814,17 +2814,17 @@ nsWindow::OnButtonReleaseEvent(GdkEventB

     LayoutDeviceIntPoint pos = event.mRefPoint;

     nsEventStatus eventStatus = DispatchInputEvent(&event);

     bool defaultPrevented = (eventStatus == nsEventStatus_eConsumeNoDefault);

     // Check if mouse position in titlebar and doubleclick happened to

     // trigger restore/maximize.

     if (!defaultPrevented

-             && mIsCSDEnabled

+             && mDrawInTitlebar

              && event.button == WidgetMouseEvent::eLeftButton

              && event.mClickCount == 2

              && mDraggableRegion.Contains(pos.x, pos.y)) {

         if (mSizeState == nsSizeMode_Maximized) {

             SetSizeMode(nsSizeMode_Normal);

         } else {

             SetSizeMode(nsSizeMode_Maximized);

@@ -3758,22 +3758,18 @@ nsWindow::Create(nsIWidget* aParent,

             gtk_window_set_wmclass(GTK_WINDOW(mShell), "Toplevel",

                                    gdk_get_program_class());

             // each toplevel window gets its own window group

             GtkWindowGroup *group = gtk_window_group_new();

             gtk_window_group_add_window(group, GTK_WINDOW(mShell));

             g_object_unref(group);

-            int32_t isCSDAvailable = false;

-            nsresult rv = LookAndFeel::GetInt(LookAndFeel::eIntID_GTKCSDAvailable,

-                                              &isCSDAvailable);

-            if (NS_SUCCEEDED(rv)) {

-               mIsCSDAvailable = isCSDAvailable;

-            }

+            // We enable titlebar rendering for toplevel windows only.

+            mCSDSupportLevel = GetSystemCSDSupportLevel();

         }

         // 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.

@@ -3788,17 +3784,17 @@ nsWindow::Create(nsIWidget* aParent,

          *    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

          *    to mContainer and we listen to the Gtk+ events on mContainer.

          */

         GtkStyleContext* style = gtk_widget_get_style_context(mShell);

         drawToContainer =

             !mIsX11Display ||

-            (mIsCSDAvailable && GetCSDSupportLevel() == CSD_SUPPORT_CLIENT) ||

+            (mCSDSupportLevel == CSD_SUPPORT_CLIENT) ||

             gtk_style_context_has_class(style, "csd");

         eventWidget = (drawToContainer) ? container : mShell;

         gtk_widget_add_events(eventWidget, kEvents);

         if (drawToContainer)

             gtk_widget_add_events(mShell, GDK_PROPERTY_CHANGE_MASK);

         // Prevent GtkWindow from painting a background to avoid flickering.

@@ -6581,90 +6577,91 @@ nsWindow::ClearCachedResources()

             window->ClearCachedResources();

         }

     }

 }

 nsresult

 nsWindow::SetNonClientMargins(LayoutDeviceIntMargin &aMargins)

 {

-  SetDrawsInTitlebar(aMargins.top == 0);

-  return NS_OK;

+    SetDrawsInTitlebar(aMargins.top == 0);

+    return NS_OK;

 }

 void

 nsWindow::SetDrawsInTitlebar(bool aState)

 {

-  if (!mIsCSDAvailable || aState == mIsCSDEnabled)

-      return;

-

-  if (mShell) {

-      if (GetCSDSupportLevel() == CSD_SUPPORT_SYSTEM) {

-          SetWindowDecoration(aState ? eBorderStyle_border : mBorderStyle);

-      }

-      else {

-          /* Window manager does not support GDK_DECOR_BORDER,

-           * emulate it by CSD.

-           *

-           * gtk_window_set_titlebar() works on unrealized widgets only,

-           * we need to handle mShell carefully here.

-           * When CSD is enabled mGdkWindow is owned by mContainer which is good

-           * as we can't delete our mGdkWindow. To make mShell unrealized while

-           * mContainer is preserved we temporary reparent mContainer to an

-           * invisible GtkWindow.

-           */

-          NativeShow(false);

-

-          // Using GTK_WINDOW_POPUP rather than

-          // GTK_WINDOW_TOPLEVEL in the hope that POPUP results in less

-          // initialization and window manager interaction.

-          GtkWidget* tmpWindow = gtk_window_new(GTK_WINDOW_POPUP);

-          gtk_widget_realize(tmpWindow);

-

-          gtk_widget_reparent(GTK_WIDGET(mContainer), tmpWindow);

-          gtk_widget_unrealize(GTK_WIDGET(mShell));

-

-          // Available as of GTK 3.10+

-          static auto sGtkWindowSetTitlebar = (void (*)(GtkWindow*, GtkWidget*))

-              dlsym(RTLD_DEFAULT, "gtk_window_set_titlebar");

-          MOZ_ASSERT(sGtkWindowSetTitlebar,

-              "Missing gtk_window_set_titlebar(), old Gtk+ library?");

-

-          if (aState) {

-              // Add a hidden titlebar widget to trigger CSD, but disable the default

-              // titlebar.  GtkFixed is a somewhat random choice for a simple unused

-              // widget. gtk_window_set_titlebar() takes ownership of the titlebar

-              // widget.

-              sGtkWindowSetTitlebar(GTK_WINDOW(mShell), gtk_fixed_new());

-          } else {

-              sGtkWindowSetTitlebar(GTK_WINDOW(mShell), nullptr);

-          }

-

-          /* A workaround for https://bugzilla.gnome.org/show_bug.cgi?id=791081

-           * gtk_widget_realize() throws:

-           * "In pixman_region32_init_rect: Invalid rectangle passed"

-           * when mShell has default 1x1 size.

-           */

-          GtkAllocation allocation = {0, 0, 0, 0};

-          gtk_widget_get_preferred_width(GTK_WIDGET(mShell), nullptr,

-                                         &allocation.width);

-          gtk_widget_get_preferred_height(GTK_WIDGET(mShell), nullptr,

-                                          &allocation.height);

-          gtk_widget_size_allocate(GTK_WIDGET(mShell), &allocation);

-

-          gtk_widget_realize(GTK_WIDGET(mShell));

-          gtk_widget_reparent(GTK_WIDGET(mContainer), GTK_WIDGET(mShell));

-          mNeedsShow = true;

-          NativeResize();

-

-          gtk_widget_destroy(tmpWindow);

-      }

-  }

-

-  mIsCSDEnabled = aState;

+    if (!mShell ||

+        mCSDSupportLevel == CSD_SUPPORT_NONE ||

+        aState == mDrawInTitlebar) {

+        return;

+    }

+

+    if (mCSDSupportLevel == CSD_SUPPORT_SYSTEM) {

+        SetWindowDecoration(aState ? eBorderStyle_border : mBorderStyle);

+    }

+    else if (mCSDSupportLevel == CSD_SUPPORT_CLIENT) {

+        /* Window manager does not support GDK_DECOR_BORDER,

+         * emulate it by CSD.

+         *

+         * gtk_window_set_titlebar() works on unrealized widgets only,

+         * we need to handle mShell carefully here.

+         * When CSD is enabled mGdkWindow is owned by mContainer which is good

+         * as we can't delete our mGdkWindow. To make mShell unrealized while

+         * mContainer is preserved we temporary reparent mContainer to an

+         * invisible GtkWindow.

+         */

+        NativeShow(false);

+

+        // Using GTK_WINDOW_POPUP rather than

+        // GTK_WINDOW_TOPLEVEL in the hope that POPUP results in less

+        // initialization and window manager interaction.

+        GtkWidget* tmpWindow = gtk_window_new(GTK_WINDOW_POPUP);

+        gtk_widget_realize(tmpWindow);

+

+        gtk_widget_reparent(GTK_WIDGET(mContainer), tmpWindow);

+        gtk_widget_unrealize(GTK_WIDGET(mShell));

+

+        // Available as of GTK 3.10+

+        static auto sGtkWindowSetTitlebar = (void (*)(GtkWindow*, GtkWidget*))

+            dlsym(RTLD_DEFAULT, "gtk_window_set_titlebar");

+        MOZ_ASSERT(sGtkWindowSetTitlebar,

+            "Missing gtk_window_set_titlebar(), old Gtk+ library?");

+

+        if (aState) {

+            // Add a hidden titlebar widget to trigger CSD, but disable the default

+            // titlebar.  GtkFixed is a somewhat random choice for a simple unused

+            // widget. gtk_window_set_titlebar() takes ownership of the titlebar

+            // widget.

+            sGtkWindowSetTitlebar(GTK_WINDOW(mShell), gtk_fixed_new());

+        } else {

+            sGtkWindowSetTitlebar(GTK_WINDOW(mShell), nullptr);

+        }

+

+        /* A workaround for https://bugzilla.gnome.org/show_bug.cgi?id=791081

+         * gtk_widget_realize() throws:

+         * "In pixman_region32_init_rect: Invalid rectangle passed"

+         * when mShell has default 1x1 size.

+         */

+        GtkAllocation allocation = {0, 0, 0, 0};

+        gtk_widget_get_preferred_width(GTK_WIDGET(mShell), nullptr,

+                                       &allocation.width);

+        gtk_widget_get_preferred_height(GTK_WIDGET(mShell), nullptr,

+                                        &allocation.height);

+        gtk_widget_size_allocate(GTK_WIDGET(mShell), &allocation);

+

+        gtk_widget_realize(GTK_WIDGET(mShell));

+        gtk_widget_reparent(GTK_WIDGET(mContainer), GTK_WIDGET(mShell));

+        mNeedsShow = true;

+        NativeResize();

+

+        gtk_widget_destroy(tmpWindow);

+    }

+

+    mDrawInTitlebar = aState;

 }

 gint

 nsWindow::GdkScaleFactor()

 {

 #if (MOZ_WIDGET_GTK >= 3)

     // Available as of GTK 3.10+

     static auto sGdkWindowGetScaleFactorPtr = (gint (*)(GdkWindow*))

@@ -6923,28 +6920,28 @@ nsWindow::SynthesizeNativeTouchPoint(uin

   event.touch.y = DevicePixelsToGdkCoordRoundDown(pointInWindow.y);

   gdk_event_put(&event);

   return NS_OK;

 }

 #endif

-bool

-nsWindow::DoDrawTitlebar() const

-{

-    return mIsCSDEnabled && mSizeState == nsSizeMode_Normal;

-}

-

 nsWindow::CSDSupportLevel

-nsWindow::GetCSDSupportLevel() {

+nsWindow::GetSystemCSDSupportLevel() {

     if (sCSDSupportLevel != CSD_SUPPORT_UNKNOWN) {

         return sCSDSupportLevel;

     }

+    // Require GTK 3.10 for GtkHeaderBar support and compatible window manager.

+    if (gtk_check_version(3, 10, 0) != nullptr) {

+        sCSDSupportLevel = CSD_SUPPORT_NONE;

+        return sCSDSupportLevel;

+    }

+

     const char* currentDesktop = getenv("XDG_CURRENT_DESKTOP");

     if (currentDesktop) {

         // GNOME Flashback (fallback)

         if (strstr(currentDesktop, "GNOME-Flashback:GNOME") != nullptr) {

             sCSDSupportLevel = CSD_SUPPORT_CLIENT;

         // gnome-shell

         } else if (strstr(currentDesktop, "GNOME") != nullptr) {

             sCSDSupportLevel = CSD_SUPPORT_SYSTEM;

diff -up firefox-60.0/widget/gtk/gtk3drawing.cpp.orig firefox-60.0/widget/gtk/gtk3drawing.cpp

--- firefox-60.0/widget/gtk/gtk3drawing.cpp.orig	2018-04-26 22:07:36.000000000 +0200

+++ firefox-60.0/widget/gtk/gtk3drawing.cpp	2018-04-30 13:38:19.083949868 +0200

@@ -38,6 +38,16 @@ static ToolbarGTKMetrics sToolbarMetrics

 #define GTK_STATE_FLAG_CHECKED (1 << 11)

 #endif

+static GtkBorder

+operator+=(GtkBorder& first, const GtkBorder& second)

+{

+    first.left += second.left;

+    first.right += second.right;

+    first.top += second.top;

+    first.bottom += second.bottom;

+    return first;

+}

+

 static gint

 moz_gtk_get_tab_thickness(GtkStyleContext *style);

@@ -3056,6 +3066,76 @@ GetScrollbarMetrics(GtkOrientation aOrie

     return metrics;

 }

+/*

+ * get_shadow_width() from gtkwindow.c is not public so we need

+ * to implement it.

+ */

+bool

+GetCSDDecorationSize(GtkWindow *aGtkWindow, GtkBorder* aDecorationSize)

+{

+    GtkStyleContext* context = gtk_widget_get_style_context(GTK_WIDGET(aGtkWindow));

+    bool solidDecorations = gtk_style_context_has_class(context, "solid-csd");

+    context = GetStyleContext(solidDecorations ?

+                              MOZ_GTK_WINDOW_DECORATION_SOLID :

+                              MOZ_GTK_WINDOW_DECORATION);

+

+    /* Always sum border + padding */

+    GtkBorder padding;

+    GtkStateFlags state = gtk_style_context_get_state(context);

+    gtk_style_context_get_border(context, state, aDecorationSize);

+    gtk_style_context_get_padding(context, state, &padding);

+    *aDecorationSize += padding;

+

+    // Available on GTK 3.20+.

+    static auto sGtkRenderBackgroundGetClip =

+        (void (*)(GtkStyleContext*, gdouble, gdouble, gdouble, gdouble, GdkRectangle*))

+        dlsym(RTLD_DEFAULT, "gtk_render_background_get_clip");

+

+    GtkBorder margin;

+    gtk_style_context_get_margin(context, state, &margin);

+

+    GtkBorder extents = {0, 0, 0, 0};

+    if (sGtkRenderBackgroundGetClip) {

+        /* Get shadow extents but combine with style margin; use the bigger value.

+         */

+        GdkRectangle clip;

+        sGtkRenderBackgroundGetClip(context, 0, 0, 0, 0, &clip);

+

+        extents.top = -clip.y;

+        extents.right = clip.width + clip.x;

+        extents.bottom = clip.height + clip.y;

+        extents.left = -clip.x;

+

+        // Margin is used for resize grip size - it's not present on

+        // popup windows.

+        if (gtk_window_get_window_type(aGtkWindow) != GTK_WINDOW_POPUP) {

+            extents.top = MAX(extents.top, margin.top);

+            extents.right = MAX(extents.right, margin.right);

+            extents.bottom = MAX(extents.bottom, margin.bottom);

+            extents.left = MAX(extents.left, margin.left);

+        }

+    } else {

+        /* If we can't get shadow extents use decoration-resize-handle instead

+         * as a workaround. This is inspired by update_border_windows()

+         * from gtkwindow.c although this is not 100% accurate as we emulate

+         * the extents here.

+         */

+        gint handle;

+        gtk_widget_style_get(GetWidget(MOZ_GTK_WINDOW),

+                             "decoration-resize-handle", &handle,

+                             NULL);

+

+        extents.top = handle + margin.top;

+        extents.right = handle + margin.right;

+        extents.bottom = handle + margin.bottom;

+        extents.left = handle + margin.left;

+    }

+

+    *aDecorationSize += extents;

+

+    return (sGtkRenderBackgroundGetClip != nullptr);

+}

+

 /* cairo_t *cr argument has to be a system-cairo. */

 gint

 moz_gtk_widget_paint(WidgetNodeType widget, cairo_t *cr,

diff -up firefox-60.0/widget/gtk/gtkdrawing.h.orig firefox-60.0/widget/gtk/gtkdrawing.h

--- firefox-60.0/widget/gtk/gtkdrawing.h.orig	2018-04-26 22:07:35.000000000 +0200

+++ firefox-60.0/widget/gtk/gtkdrawing.h	2018-04-30 13:38:19.083949868 +0200

@@ -334,6 +334,10 @@ typedef enum {

    */

   MOZ_GTK_HEADER_BAR_BUTTON_MAXIMIZE_RESTORE,

+  /* Client-side window decoration node. Available on GTK 3.20+. */

+  MOZ_GTK_WINDOW_DECORATION,

+  MOZ_GTK_WINDOW_DECORATION_SOLID,

+

   MOZ_GTK_WIDGET_NODE_COUNT

 } WidgetNodeType;

@@ -606,4 +610,17 @@ GetToolbarButtonMetrics(WidgetNodeType a

 int

 GetGtkHeaderBarButtonLayout(WidgetNodeType* aButtonLayout, int aMaxButtonNums);

+/**

+ * Get size of CSD window extents of given GtkWindow.

+ *

+ * aGtkWindow      [IN]  Decorated window.

+ * aDecorationSize [OUT] Returns calculated (or estimated) decoration

+ *                       size of given aGtkWindow.

+ *

+ * returns:    True if we have extract decoration size (for GTK 3.20+)

+ *             False if we have only an estimation (for GTK+ before  3.20+)

+ */

+bool

+GetCSDDecorationSize(GtkWindow *aGtkWindow, GtkBorder* aDecorationSize);

+

 #endif

diff -up firefox-60.0/widget/gtk/nsWindow.cpp.orig firefox-60.0/widget/gtk/nsWindow.cpp

--- firefox-60.0/widget/gtk/nsWindow.cpp.orig	2018-04-30 13:37:32.145122854 +0200

+++ firefox-60.0/widget/gtk/nsWindow.cpp	2018-04-30 13:39:12.593752681 +0200

@@ -127,6 +127,7 @@ using namespace mozilla::widget;

 #endif

 #include "nsShmImage.h"

+#include "gtkdrawing.h"

 #include "nsIDOMWheelEvent.h"

@@ -3360,6 +3361,10 @@ nsWindow::OnWindowStateEvent(GtkWidget *

           aEvent->new_window_state & GDK_WINDOW_STATE_FULLSCREEN);

       }

     }

+

+    if (mDrawInTitlebar && mCSDSupportLevel == CSD_SUPPORT_CLIENT) {

+        UpdateClientOffsetForCSDWindow();

+    }

 }