--- a/modules/libpref/init/all.js
+++ b/modules/libpref/init/all.js
@@ -4701,16 +4701,17 @@ pref("gfx.content.always-paint", false);
 
 #ifdef ANDROID
 pref("gfx.apitrace.enabled",false);
 #endif
 
 #ifdef MOZ_X11
 #ifdef MOZ_WIDGET_GTK
 pref("gfx.xrender.enabled",false);
+pref("widget.allow-gtk-dark-theme", false);
 #endif
 #endif
 
 #ifdef XP_WIN
 // Whether to disable the automatic detection and use of direct2d.
 pref("gfx.direct2d.disabled", false);
 
 // Whether to attempt to enable Direct2D regardless of automatic detection or

--- a/widget/gtk/nsLookAndFeel.cpp
+++ b/widget/gtk/nsLookAndFeel.cpp
@@ -1148,17 +1148,21 @@ nsLookAndFeel::EnsureInit()
         // 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);
 
-        if (dark && !PR_GetEnv("MOZ_ALLOW_GTK_DARK_THEME")) {
+        bool allowDarkEnv = PR_GetEnv("MOZ_ALLOW_GTK_DARK_THEME") != nullptr;
+        bool allowDarkPref =
+            mozilla::Preferences::GetBool("widget.allow-gtk-dark-theme", false);
+
+        if (dark && !allowDarkEnv && !allowDarkPref) {
             g_object_set(settings, dark_setting, FALSE, nullptr);
         }
     }
 
     // Scrollbar colors
     style = ClaimStyleContext(MOZ_GTK_SCROLLBAR_TROUGH_VERTICAL);
     gtk_style_context_get_background_color(style, GTK_STATE_FLAG_NORMAL, &color);
     sMozScrollbar = GDK_RGBA_TO_NS_RGBA(color);