--- a/dom/ipc/ContentChild.cpp
+++ b/dom/ipc/ContentChild.cpp
@@ -196,16 +196,21 @@
 #include "mozilla/widget/PuppetBidiKeyboard.h"
 #include "mozilla/RemoteSpellCheckEngineChild.h"
 #include "GMPServiceChild.h"
 #include "GfxInfoBase.h"
 #include "gfxPlatform.h"
 #include "nscore.h" // for NS_FREE_PERMANENT_DATA
 #include "VRManagerChild.h"
 
+#ifdef MOZ_WIDGET_GTK
+#include "nsAppRunner.h"
+#endif
+
+
 using namespace mozilla;
 using namespace mozilla::docshell;
 using namespace mozilla::dom::devicestorage;
 using namespace mozilla::dom::ipc;
 using namespace mozilla::dom::workers;
 using namespace mozilla::media;
 using namespace mozilla::embedding;
 using namespace mozilla::gmp;
@@ -508,26 +513,26 @@ ContentChild::Init(MessageLoop* aIOLoop,
                    IPC::Channel* aChannel)
 {
 #ifdef MOZ_WIDGET_GTK
   // We need to pass a display down to gtk_init because it's not going to
   // use the one from the environment on its own when deciding which backend
   // to use, and when starting under XWayland, it may choose to start with
   // the wayland backend instead of the x11 backend.
   // The DISPLAY environment variable is normally set by the parent process.
-  char* display_name = PR_GetEnv("DISPLAY");
+  const char* display_name = DetectDisplay();
   if (display_name) {
     int argc = 3;
     char option_name[] = "--display";
     char* argv[] = {
       // argv0 is unused because g_set_prgname() was called in
       // XRE_InitChildProcess().
       nullptr,
       option_name,
-      display_name,
+      const_cast<char*>(display_name),
       nullptr
     };
     char** argvp = argv;
     gtk_init(&argc, &argvp);
   } else {
     gtk_init(nullptr, nullptr);
   }
 #endif

--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -2887,17 +2887,17 @@ static void MOZ_gdk_display_close(GdkDis
   }
 #else // not CLEANUP_MEMORY
   // Don't do anything to avoid running into driver bugs under XCloseDisplay().
   // See bug 973192.
   (void) display;
 #endif
 }
 
-static const char* detectDisplay(void)
+const char* DetectDisplay(void)
 {
   bool tryX11 = false;
   bool tryWayland = false;
   bool tryBroadway = false;
 
   // Honor user backend selection
   const char *backend = PR_GetEnv("GDK_BACKEND");
   if (!backend || strstr(backend, "*")) {
@@ -3745,17 +3745,17 @@ XREMain::XRE_mainStartup(bool* aExitFlag
 
 #if defined(MOZ_WIDGET_GTK)
   // display_name is owned by gdk.
   const char *display_name = gdk_get_display_arg_name();
   bool saveDisplayArg = false;
   if (display_name) {
     saveDisplayArg = true;
   } else {
-    display_name = detectDisplay();
+    display_name = DetectDisplay();
     if (!display_name) {
       return 1;
     }
   }
 #endif /* MOZ_WIDGET_GTK */
 #ifdef MOZ_X11
   // Init X11 in thread-safe mode. Must be called prior to the first call to XOpenDisplay
   // (called inside gdk_display_open). This is a requirement for off main tread compositing.

--- a/toolkit/xre/nsAppRunner.h
+++ b/toolkit/xre/nsAppRunner.h
@@ -128,9 +128,13 @@ void SetupErrorHandling(const char* prog
 
 /**
  * A numeric value indicating whether multiprocess might be blocked.
  * Possible values can be found at nsAppRunner.cpp. A value of 0
  * represents not blocking.
  */
 uint32_t MultiprocessBlockPolicy();
 
+#ifdef MOZ_WIDGET_GTK
+const char* DetectDisplay();
+#endif
+
 #endif // nsAppRunner_h__