diff --git a/toolkit/xre/nsAppRunner.cpp b/toolkit/xre/nsAppRunner.cpp
index c4220ffd385..45123127f5c 100644
--- a/toolkit/xre/nsAppRunner.cpp
+++ b/toolkit/xre/nsAppRunner.cpp
@@ -231,6 +231,7 @@ static char **gQtOnlyArgv;
 #endif
 
 #if defined(MOZ_WIDGET_GTK)
+#include <glib.h>
 #if defined(DEBUG) || defined(NS_BUILD_REFCNT_LOGGING)
 #define CLEANUP_MEMORY 1
 #define PANGO_ENABLE_BACKEND
@@ -4287,6 +4288,25 @@ XREMain::XRE_mainRun()
   return rv;
 }
 
+#if MOZ_WIDGET_GTK == 2
+void XRE_GlibInit()
+{
+  static bool ran_once = false;
+
+  // glib < 2.24 doesn't want g_thread_init to be invoked twice, so ensure
+  // we only do it once. No need for thread safety here, since this is invoked
+  // well before any thread is spawned.
+  if (!ran_once) {
+    // glib version < 2.36 doesn't initialize g_slice in a static initializer.
+    // Ensure this happens through g_thread_init (glib version < 2.32) or
+    // g_type_init (2.32 <= gLib version < 2.36)."
+    g_thread_init(nullptr);
+    g_type_init();
+    ran_once = true;
+  }
+}
+#endif
+
 /*
  * XRE_main - A class based main entry point used by most platforms.
  *            Note that on OSX, aAppData->xreDirectory will point to
@@ -4325,14 +4345,8 @@ XREMain::XRE_main(int argc, char* argv[], const nsXREAppData* aAppData)
 
   mozilla::IOInterposerInit ioInterposerGuard;
 
-#if defined(MOZ_WIDGET_GTK)
-#if defined(MOZ_MEMORY) || defined(__FreeBSD__) || defined(__NetBSD__)
-  // Disable the slice allocator, since jemalloc already uses similar layout
-  // algorithms, and using a sub-allocator tends to increase fragmentation.
-  // This must be done before g_thread_init() is called.
-  g_slice_set_config(G_SLICE_CONFIG_ALWAYS_MALLOC, 1);
-#endif
-  g_thread_init(nullptr);
+#if MOZ_WIDGET_GTK == 2
+  XRE_GlibInit();
 #endif
 
   // init
diff --git a/toolkit/xre/nsEmbedFunctions.cpp b/toolkit/xre/nsEmbedFunctions.cpp
index b6fb2ecc293..d4a7c75e6c9 100644
--- a/toolkit/xre/nsEmbedFunctions.cpp
+++ b/toolkit/xre/nsEmbedFunctions.cpp
@@ -466,8 +466,8 @@ XRE_InitChildProcess(int aArgc,
 #ifdef MOZ_X11
   XInitThreads();
 #endif
-#if defined(MOZ_WIDGET_GTK)
-  g_thread_init(nullptr);
+#if MOZ_WIDGET_GTK == 2
+  XRE_GlibInit();
 #endif
 
 #if defined(MOZ_WIDGET_QT)
diff --git a/xpcom/build/nsXULAppAPI.h b/xpcom/build/nsXULAppAPI.h
index 975b7b21fa3..a4c0067bcd0 100644
--- a/xpcom/build/nsXULAppAPI.h
+++ b/xpcom/build/nsXULAppAPI.h
@@ -477,4 +477,9 @@ XRE_API(void,
 XRE_API(int,
         XRE_XPCShellMain, (int argc, char** argv, char** envp))
 
+#if MOZ_WIDGET_GTK == 2
+XRE_API(void,
+        XRE_GlibInit, ())
+#endif
+
 #endif // _nsXULAppAPI_h__
diff --git a/xpcom/glue/standalone/moz.build b/xpcom/glue/standalone/moz.build
index 47a2d6e0112..4f24c50a31d 100644
--- a/xpcom/glue/standalone/moz.build
+++ b/xpcom/glue/standalone/moz.build
@@ -54,3 +54,6 @@ USE_LIBS += [
 NO_EXPAND_LIBS = True
 
 DIST_INSTALL = True
+
+if CONFIG['MOZ_WIDGET_TOOLKIT'] in ('gtk2', 'gtk3'):
+    CXXFLAGS += CONFIG['GLIB_CFLAGS']
diff --git a/xpcom/glue/standalone/nsXPCOMGlue.cpp b/xpcom/glue/standalone/nsXPCOMGlue.cpp
index eac10e5f0e0..7654d64937e 100644
--- a/xpcom/glue/standalone/nsXPCOMGlue.cpp
+++ b/xpcom/glue/standalone/nsXPCOMGlue.cpp
@@ -426,9 +426,55 @@ XPCOMGlueEnablePreload()
   do_preload = true;
 }
 
+#if defined(MOZ_WIDGET_GTK) && (defined(MOZ_MEMORY) || defined(__FreeBSD__) || defined(__NetBSD__))
+#define MOZ_GSLICE_INIT
+#endif
+
+#ifdef MOZ_GSLICE_INIT
+#include <glib.h>
+
+class GSliceInit {
+public:
+  GSliceInit() {
+    mHadGSlice = bool(getenv("G_SLICE"));
+    if (!mHadGSlice) {
+      // Disable the slice allocator, since jemalloc already uses similar layout
+      // algorithms, and using a sub-allocator tends to increase fragmentation.
+      // This must be done before g_thread_init() is called.
+      // glib >= 2.36 initializes g_slice as a side effect of its various static
+      // initializers, so this needs to happen before glib is loaded, which is
+      // this is hooked in XPCOMGlueStartup before libxul is loaded. This
+      // relies on the main executable not depending on glib.
+      setenv("G_SLICE", "always-malloc", 1);
+    }
+  }
+
+  ~GSliceInit() {
+#if MOZ_WIDGET_GTK == 2
+    if (sTop) {
+      auto XRE_GlibInit = (void (*)(void)) GetSymbol(sTop->libHandle,
+        "XRE_GlibInit");
+      // Initialize glib enough for G_SLICE to have an effect before it is unset.
+      // unset.
+      XRE_GlibInit();
+    }
+#endif
+    if (!mHadGSlice) {
+      unsetenv("G_SLICE");
+    }
+  }
+
+private:
+  bool mHadGSlice;
+};
+#endif
+
 nsresult
 XPCOMGlueStartup(const char* aXPCOMFile)
 {
+#ifdef MOZ_GSLICE_INIT
+  GSliceInit gSliceInit;
+#endif
   xpcomFunctions.version = XPCOM_GLUE_VERSION;
   xpcomFunctions.size    = sizeof(XPCOMFunctions);