Re-land this part of bug 305949 now that I've configure-tested the broken compiler (bug 334866)

xpcom/glue/nsWeakReference.h

@@ -49,10 +49,8 @@ class nsWeakReference;
 
 // Set IMETHOD_VISIBILITY to empty so that the class-level NS_COM declaration
 // controls member method visibility.
-// XXXbsmedberg reverted to use NS_VISIBILITY_DEFAULT because this is exposing
-// http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26905
 #undef  IMETHOD_VISIBILITY
-#define IMETHOD_VISIBILITY NS_VISIBILITY_DEFAULT
+#define IMETHOD_VISIBILITY
 
 class NS_COM_GLUE nsSupportsWeakReference : public nsISupportsWeakReference
   {