diff -up firefox-52.0/modules/libpref/init/all.js.1158076 firefox-52.0/modules/libpref/init/all.js

--- firefox-52.0/modules/libpref/init/all.js.1158076	2017-03-22 10:05:22.318067553 +0100

+++ firefox-52.0/modules/libpref/init/all.js	2017-03-22 10:07:15.360555913 +0100

@@ -4646,6 +4646,7 @@ pref("gfx.apitrace.enabled",false);

 pref("gfx.content.use-native-pushlayer", true);

 #ifdef MOZ_WIDGET_GTK

 pref("gfx.xrender.enabled",false);

+pref("widget.allow-gtk-dark-theme", false);

 #endif

 #endif

diff -up firefox-52.0/widget/gtk/mozgtk/mozgtk.c.1158076 firefox-52.0/widget/gtk/mozgtk/mozgtk.c

--- firefox-52.0/widget/gtk/mozgtk/mozgtk.c.1158076	2017-03-22 10:05:22.313067576 +0100

+++ firefox-52.0/widget/gtk/mozgtk/mozgtk.c	2017-03-22 10:08:34.122199432 +0100

@@ -522,6 +522,7 @@ STUB(gdk_x11_display_get_type)

 STUB(gtk_box_new)

 STUB(gtk_cairo_should_draw_window)

 STUB(gtk_cairo_transform_to_window)

+STUB(gtk_css_provider_get_named)

 STUB(gtk_combo_box_text_append)

 STUB(gtk_drag_set_icon_surface)

 STUB(gtk_get_major_version)

@@ -548,6 +549,7 @@ STUB(gtk_scale_new)

 STUB(gtk_scrollbar_new)

 STUB(gtk_style_context_add_class)

 STUB(gtk_style_context_add_region)

+STUB(gtk_style_context_add_provider_for_screen)

 STUB(gtk_style_context_get)

 STUB(gtk_style_context_get_background_color)

 STUB(gtk_style_context_get_border)

@@ -573,6 +575,7 @@ STUB(gtk_style_context_set_path)

 STUB(gtk_style_context_set_parent)

 STUB(gtk_style_context_set_state)

 STUB(gtk_style_properties_lookup_property)

+STUB(gtk_style_provider_get_type)

 STUB(gtk_tree_view_column_get_button)

 STUB(gtk_widget_get_preferred_size)

 STUB(gtk_widget_get_state_flags)

diff -up firefox-52.0/widget/gtk/nsLookAndFeel.cpp.1158076 firefox-52.0/widget/gtk/nsLookAndFeel.cpp

--- firefox-52.0/widget/gtk/nsLookAndFeel.cpp.1158076	2017-03-22 10:05:22.314067571 +0100

+++ firefox-52.0/widget/gtk/nsLookAndFeel.cpp	2017-03-22 10:07:56.914367838 +0100

@@ -50,9 +50,9 @@ nsLookAndFeel::nsLookAndFeel()

       mStyle(nullptr),

 #endif

       mDefaultFontCached(false), mButtonFontCached(false),

-      mFieldFontCached(false), mMenuFontCached(false)

+      mFieldFontCached(false), mMenuFontCached(false),

+      mInitialized(false)

 {

-    Init();    

 }

 nsLookAndFeel::~nsLookAndFeel()

@@ -224,6 +224,8 @@ GetBorderColors(GtkStyleContext* aContex

 nsresult

 nsLookAndFeel::NativeGetColor(ColorID aID, nscolor& aColor)

 {

+    EnsureInit();

+

 #if (MOZ_WIDGET_GTK == 3)

     GdkRGBA gdk_color;

 #endif

@@ -675,6 +677,8 @@ nsLookAndFeel::GetIntImpl(IntID aID, int

         return res;

     res = NS_OK;

+    // We use delayed initialization by EnsureInit() here

+    // to ensure mozilla::Preferences is available (see Bug 1158076).

     switch (aID) {

     case eIntID_CaretBlinkTime:

         {

@@ -837,6 +841,7 @@ nsLookAndFeel::GetIntImpl(IntID aID, int

         aResult = NS_STYLE_TEXT_DECORATION_STYLE_WAVY;

         break;

     case eIntID_MenuBarDrag:

+        EnsureInit();

         aResult = sMenuSupportsDrag;

         break;

     case eIntID_ScrollbarButtonAutoRepeatBehavior:

@@ -877,6 +882,7 @@ nsLookAndFeel::GetFloatImpl(FloatID aID,

         aResult = 1.0f;

         break;

     case eFloatID_CaretAspectRatio:

+        EnsureInit();

         aResult = sCaretRatio;

         break;

     default:

@@ -1057,11 +1063,15 @@ nsLookAndFeel::GetFontImpl(FontID aID, n

 }

 void

-nsLookAndFeel::Init()

+nsLookAndFeel::EnsureInit()

 {

     GdkColor colorValue;

     GdkColor *colorValuePtr;

+    if (mInitialized)

+        return;

+    mInitialized = true;

+

 #if (MOZ_WIDGET_GTK == 2)

     NS_ASSERTION(!mStyle, "already initialized");

     // GtkInvisibles come with a refcount that is not floating

@@ -1133,17 +1143,40 @@ nsLookAndFeel::Init()

     // ask Gtk to create it explicitly. Otherwise we may end up

     // with wrong color theme, see Bug 972382

     GtkSettings *settings = gtk_settings_get_for_screen(gdk_screen_get_default());

+    bool e10sActive = mozilla::BrowserTabsRemoteAutostart();

+

+    if (!e10sActive || XRE_IsContentProcess()) {

+        // Disable dark theme in processes with web content because it

+        // interacts poorly with widget styling (see bug 1216658).

+        // To avoid triggering reload of theme settings unnecessarily, only set the

+        // setting when necessary.

+        const gchar* dark_setting = "gtk-application-prefer-dark-theme";

+        gboolean dark;

+        g_object_get(settings, dark_setting, &dark, nullptr);

+

+        bool allowDarkEnv = PR_GetEnv("MOZ_ALLOW_GTK_DARK_THEME") != nullptr;

+        bool allowDarkPref =

+            mozilla::Preferences::GetBool("widget.allow-gtk-dark-theme", false);

-    // Disable dark theme because it interacts poorly with widget styling in

-    // web content (see bug 1216658).

-    // To avoid triggering reload of theme settings unnecessarily, only set the

-    // setting when necessary.

-    const gchar* dark_setting = "gtk-application-prefer-dark-theme";

-    gboolean dark;

-    g_object_get(settings, dark_setting, &dark, nullptr);

+        if (dark && !allowDarkEnv && !allowDarkPref) {

+            g_object_set(settings, dark_setting, FALSE, nullptr);

+        }

-    if (dark && !PR_GetEnv("MOZ_ALLOW_GTK_DARK_THEME")) {

-        g_object_set(settings, dark_setting, FALSE, nullptr);

+        // Allow Gtk+ theme override for web content only.

+        if (e10sActive) {

+            auto contentThemeName =

+                mozilla::Preferences::GetCString("widget.content-gtk-theme");

+            if (!contentThemeName.IsEmpty()) {

+                // TODO: It should be enough to change theme by "gtk-theme-name"

+                // settings but that does not have any effect here. Maybe we

+                // call it too late?

+                GtkCssProvider *styleProvider =

+                    gtk_css_provider_get_named(contentThemeName, NULL);

+                gtk_style_context_add_provider_for_screen(gdk_screen_get_default(),

+                    GTK_STYLE_PROVIDER(styleProvider),

+                    GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);

+            }

+        }

     }

     // Scrollbar colors

@@ -1439,6 +1472,7 @@ nsLookAndFeel::Init()

 char16_t

 nsLookAndFeel::GetPasswordCharacterImpl()

 {

+    EnsureInit();

     return sInvisibleCharacter;

 }

@@ -1457,7 +1491,7 @@ nsLookAndFeel::RefreshImpl()

     mStyle = nullptr;

 #endif

-    Init();

+    mInitialized = false;

 }

 bool

diff -up firefox-52.0/widget/gtk/nsLookAndFeel.h.1158076 firefox-52.0/widget/gtk/nsLookAndFeel.h

--- firefox-52.0/widget/gtk/nsLookAndFeel.h.1158076	2016-05-12 19:13:34.000000000 +0200

+++ firefox-52.0/widget/gtk/nsLookAndFeel.h	2017-03-22 10:06:36.461731972 +0100

@@ -84,8 +84,9 @@ protected:

     char16_t sInvisibleCharacter;

     float   sCaretRatio;

     bool    sMenuSupportsDrag;

+    bool    mInitialized;

-    void Init();

+    void EnsureInit();

 };

 #endif