diff --git a/toolkit/xre/glxtest.cpp b/toolkit/xre/glxtest.cpp
index 09d5126e2784..907cf43a47ab 100644
--- a/toolkit/xre/glxtest.cpp
+++ b/toolkit/xre/glxtest.cpp
@@ -209,7 +209,7 @@ static void glxtest()
   const GLubyte *vendorString = glGetString(GL_VENDOR);
   const GLubyte *rendererString = glGetString(GL_RENDERER);
   const GLubyte *versionString = glGetString(GL_VERSION);
-  
+
   if (!vendorString || !rendererString || !versionString)
     fatal_error("glGetString returned null");
 
@@ -229,7 +229,16 @@ static void glxtest()
   glXDestroyContext(dpy, context);
   XDestroyWindow(dpy, window);
   XFreeColormap(dpy, swa.colormap);
+
+#ifdef NS_FREE_PERMANENT_DATA // conditionally defined in nscore.h, don't forget to #include it above
   XCloseDisplay(dpy);
+#else
+  // This XSync call wanted to be instead:
+  //   XCloseDisplay(dpy);
+  // but this can cause 1-minute stalls on certain setups using Nouveau, see bug 973192
+  XSync(dpy, False);
+#endif
+
   dlclose(libgl);
 
   ///// Finally write data to the pipe